arm: Replace CONFIG_CPU_CORTEX_M0_M0PLUS with CONFIG_ARMV6_M

Precursor patches have arranged all conditional compilation hanging on
CONFIG_CPU_CORTEX_M0_M0PLUS such that it actually represents support
for ARM ARMv6-M, rename the config variable to reflect this.

Change-Id: I553fcf3e606b350a9e823df31bac96636be1504f
Signed-off-by: Marcus Shawcroft <marcus.shawcroft@arm.com>
16 files changed