arm: msm: allow ARCH_MSM to have v7 cpus

ARCH_MSM supports armv7 cpus, so we're pushed the CPU_V6/CPU_V7 selection
down into the arch/arm/mach-msm/Kconfig.

Also update the description to be a bit more accurate.

Signed-off-by: Daniel Walker <dwalker@codeaurora.org>