cache: Introduce external cache controller system support

The cache API currently shipped in Zephyr is assuming that the cache
controller is always on-core thus managed at the arch level. This is not
always the case because many SoCs rely on external cache controllers as
a peripheral external to the core (for example PL310 cache controller
and the L2Cxxx family). In some cases you also want a single driver to
control a whole set of cache controllers.

Rework the cache code introducing support for external cache
controllers.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>

drivers/cache/CMakeLists.txt

@@ -0,0 +1 @@
+# SPDX-License-Identifier: Apache-2.0

drivers/cache/Kconfig

@@ -0,0 +1,18 @@
+# Copyright (c) 2021 Carlo Caione <ccaione@baylibre.com>
+# SPDX-License-Identifier: Apache-2.0
+
+menuconfig CACHE
+	bool "External cache controllers drivers"
+	help
+	  Enable support for external cache controllers drivers
+
+if CACHE
+
+module = CACHE
+module-str = cache
+source "subsys/logging/Kconfig.template.log_config"
+
+config CACHE_HAS_DRIVER
+	bool
+
+endif # CACHE