msm: Change semantics of cpu_is_msm8930()

Per revised design decisions, cpu_is_msm8930() shall only
return true on 8930, and not on the 8627 variant. Modify
the cpu_is_xxx functions to reflect this change, and update
call sites accordingly.

Change-Id: I50b943f80c731717e6cd5d7fffb13aeec0f85a40
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>