[ARM] msm: rename ARCH_MSM7X00A to ARCH_MSM

The MSM architecture covers a wider family of chips than just the MSM7X00A.
Move to a more generic name, in perparation for supporting the specific
SoC variants as sub-architectures (ARCH_MSM7X01A, ARCH_MSM722X, etc).  This
gives us ARCH_MSM for the (many) common peripherals.

This also removes the unused/obsolete config item MSM7X00A_IDLE.

Signed-off-by: Brian Swetland <swetland@google.com>