msm: pm: Rename power management module to msm-pm

pm-8x60 doesn't accurately reflect the current list of targets that
are supported. Rename them to msm-pm to be more inline with the
msm chipsets. As a part of the rename, also rename the device tree node
and the CONFIG parameters.

Change-Id: Iefa8150885f8da136de7cba4a122ec901a171a02
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>