arm: armv7m: Clean up some thumb / compiler flag options

- The correct way to build with thumb mode is to select SYS_THUMB_BUILD
- We should be setting -march=armv7-m in arch/arm/Makefile not the
  sub-config.mk file.

Signed-off-by: Tom Rini <trini@konsulko.com>

arch/arm/Kconfig

@@ -221,6 +221,7 @@ config CPU_V7M
 	select THUMB2_KERNEL
 	select SYS_CACHE_SHIFT_5
 	select SYS_ARM_MPU
+	select SYS_THUMB_BUILD
 
 config CPU_V7R
 	bool

arch/arm/Makefile

@@ -16,6 +16,7 @@ arch-$(CONFIG_CPU_ARM1136)	=-march=armv5
 arch-$(CONFIG_CPU_ARM1176)	=-march=armv5t
 arch-$(CONFIG_CPU_V7A)		=$(call cc-option, -march=armv7-a, \
 				 $(call cc-option, -march=armv7, -march=armv5))
+arch-$(CONFIG_CPU_V7M)		=-march=armv7-m
 arch-$(CONFIG_CPU_V7R)		=-march=armv7-r
 arch-$(CONFIG_ARM64)		=-march=armv8-a
 

arch/arm/cpu/armv7m/config.mk

@@ -3,4 +3,4 @@
 # (C) Copyright 2015
 # Kamil Lulko, <kamil.lulko@gmail.com>
 
-PLATFORM_CPPFLAGS += -march=armv7-m -mthumb -mno-unaligned-access
+PLATFORM_CPPFLAGS += -mno-unaligned-access