arm: Add ARMv8-M aarch32 support

Add configuration for ARMv8-M aarch32 core, which are currently
Cortex-M23/M33 cores. These cores are treated similar to ARMv7-M
cores, except the code has to be compiled with matching compiler
-march=armv8-m.main flag . These cores have no MMU, they have MPU,
which is currently not configured.

Unlike ARMv7-M, these cores have 512 interrupt vectors. While the
SYS_ARM_ARCH should be set to 8, it is set to 7 because all of the
initialization code is built from arch/arm/cpu/armv7m and not armv8.
Furthermore, CONFIG_ARM64 must be disabled, although DTs for devices
using these cores do come from arch/arm64/boot/dts.

To avoid excess duplication in Makefiles, introduce one new Kconfig
symbol, CPU_V7M_V8M. The CPU_V7M_V8M cover both ARMv7-M and ARMv8-M
cores.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Acked-by: Udit Kumar <u-kumar1@ti.com>

dts/Makefile

@@ -11,11 +11,15 @@ DEVICE_TREE := unset
 endif
 
 ifeq ($(CONFIG_OF_UPSTREAM),y)
+ifeq ($(CONFIG_CPU_V8M),y)
+dt_dir := dts/upstream/src/arm64
+else
 ifeq ($(CONFIG_ARM64),y)
 dt_dir := dts/upstream/src/arm64
 else
 dt_dir := dts/upstream/src/$(ARCH)
 endif
+endif
 else
 dt_dir := arch/$(ARCH)/dts
 endif