Bluetooth: Host: Remove printk dependency from settings

Some modules use snprintk to format the settings keys. Unfortunately
snprintk is tied with printk which is very large for some embedded
systems.
To be able to have settings enabled without also enabling printk
support, change creation of settings key strings to use bin2hex, strlen
and strcpy instead.
A utility function to make decimal presentation of a byte value is
added as u8_to_dec in lib/os/dec.c
Add new Kconfig setting BT_SETTINGS_USE_PRINTK

Signed-off-by: Kim Sekkelund <ksek@oticon.com>

tests/lib/sys/util/CMakeLists.txt

@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.13.1)
+include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
+project(lib_sys_util_tests)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})

tests/lib/sys/util/prj.conf

@@ -0,0 +1 @@
+CONFIG_ZTEST=y

tests/lib/sys/util/src/main.c

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2019 Oticon A/S
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <ztest.h>
+#include <sys/util.h>
+#include <string.h>
+
+/**
+ * @brief Test of u8_to_dec
+ *
+ * This test verifies conversion of various input values.
+ *
+ */
+static void test_u8_to_dec(void)
+{
+	char text[4];
+	u8_t len;
+
+	len = u8_to_dec(text, sizeof(text), 0);
+	zassert_equal(len, 1, "Length of 0 is not 1");
+	zassert_equal(strcmp(text, "0"), 0,
+		      "Value=0 is not converted to \"0\"");
+
+	len = u8_to_dec(text, sizeof(text), 1);
+	zassert_equal(len, 1, "Length of 1 is not 1");
+	zassert_equal(strcmp(text, "1"), 0,
+		      "Value=1 is not converted to \"1\"");
+
+	len = u8_to_dec(text, sizeof(text), 11);
+	zassert_equal(len, 2, "Length of 11 is not 2");
+	zassert_equal(strcmp(text, "11"), 0,
+		      "Value=10 is not converted to \"11\"");
+
+	len = u8_to_dec(text, sizeof(text), 100);
+	zassert_equal(len, 3, "Length of 100 is not 3");
+	zassert_equal(strcmp(text, "100"), 0,
+		      "Value=100 is not converted to \"100\"");
+
+	len = u8_to_dec(text, sizeof(text), 101);
+	zassert_equal(len, 3, "Length of 101 is not 3");
+	zassert_equal(strcmp(text, "101"), 0,
+		      "Value=101 is not converted to \"101\"");
+
+	len = u8_to_dec(text, sizeof(text), 255);
+	zassert_equal(len, 3, "Length of 255 is not 3");
+	zassert_equal(strcmp(text, "255"), 0,
+		      "Value=255 is not converted to \"255\"");
+
+	memset(text, 0, sizeof(text));
+	len = u8_to_dec(text, 2, 123);
+	zassert_equal(len, 2,
+		      "Length of converted value using 2 byte buffer isn't 2");
+	zassert_equal(
+		strcmp(text, "12"), 0,
+		"Value=123 is not converted to \"12\" using 2-byte buffer");
+
+	memset(text, 0, sizeof(text));
+	len = u8_to_dec(text, 1, 123);
+	zassert_equal(len, 1,
+		      "Length of converted value using 1 byte buffer isn't 1");
+	zassert_equal(
+		strcmp(text, "1"), 0,
+		"Value=123 is not converted to \"1\" using 1-byte buffer");
+
+	memset(text, 0, sizeof(text));
+	len = u8_to_dec(text, 0, 123);
+	zassert_equal(len, 0,
+		      "Length of converted value using 0 byte buffer isn't 0");
+}
+
+void test_main(void)
+{
+	ztest_test_suite(test_lib_sys_util_tests,
+		ztest_unit_test(test_u8_to_dec)
+	);
+
+	ztest_run_test_suite(test_lib_sys_util_tests);
+}

tests/lib/sys/util/testcase.yaml

@@ -0,0 +1,3 @@
+tests:
+  libraries.sys.util.dec:
+    tags: lib_sys_util_tests