soc: arm: nordic_nrf: unrevert provide custom busy_wait implementations

This reverts commit bd24b31139.

While the test case failure described in #14186 is associated with the
cycle-based busy-wait implementation, that test is fragile, and fails
less frequently once the incongruence between ticks-per-second and the
32 KiHz RTC clock are resolved.  It also assumes that the system clock
is more stable than the infrastructure underlying the the busy-wait
implementation, which is not necessarily true.

The gross inaccuracies in the standard busy-wait on Nordic described in
issue #11626 justify restoring the custom solution.

As this applies to all Nordic devices, move the setting to the top-level
Kconfig.defconfig.

See: https://github.com/zephyrproject-rtos/zephyr/issues/11626#issuecomment-487243369

Signed-off-by: Peter A. Bigot <pab@pabigot.com>

soc/arm/nordic_nrf/Kconfig.defconfig

@@ -17,6 +17,9 @@ config SYS_CLOCK_TICKS_PER_SEC
 	int
 	default 128
 
+config ARCH_HAS_CUSTOM_BUSY_WAIT
+	default y
+
 config BUILD_OUTPUT_HEX
 	default y
 

soc/arm/nordic_nrf/nrf51/soc.c

@@ -59,4 +59,16 @@ static int nordicsemi_nrf51_init(struct device *arg)
 	return 0;
 }
 
+#define DELAY_CALL_OVERHEAD_US 2
+
+void z_arch_busy_wait(u32_t time_us)
+{
+	if (time_us <= DELAY_CALL_OVERHEAD_US) {
+		return;
+	}
+
+	time_us -= DELAY_CALL_OVERHEAD_US;
+	nrfx_coredep_delay_us(time_us);
+}
+
 SYS_INIT(nordicsemi_nrf51_init, PRE_KERNEL_1, 0);

soc/arm/nordic_nrf/nrf52/soc.c

@@ -81,4 +81,9 @@ static int nordicsemi_nrf52_init(struct device *arg)
 	return 0;
 }
 
+void z_arch_busy_wait(u32_t time_us)
+{
+	nrfx_coredep_delay_us(time_us);
+}
+
 SYS_INIT(nordicsemi_nrf52_init, PRE_KERNEL_1, 0);

soc/arm/nordic_nrf/nrf91/Kconfig.defconfig.series

@@ -12,9 +12,6 @@ source "soc/arm/nordic_nrf/nrf91/Kconfig.defconfig.nrf91*"
 config SOC_SERIES
 	default "nrf91"
 
-config ARCH_HAS_CUSTOM_BUSY_WAIT
-	default y
-
 config SYS_POWER_MANAGEMENT
 	default y