arm: Replace CONFIG_CPU_CORTEX_M3_M4 with CONFIG_ARMV7_M

Precursor patches have arranged that conditional compilation hanging
on CONFIG_CPU_CORTEX_M3_M4 provides support for ARMv7-M, rename the
config variable to reflect this.

Change-Id: Ifa56e3c1c04505d061b2af3aec9d8b9e55b5853d
Signed-off-by: Marcus Shawcroft <marcus.shawcroft@arm.com>
18 files changed