time: alarmtimer: include lpm-levels for MSM targets only

lpm-level headers required only when CONFIG_MSM_PM is set.

To compile msm kernel for other targets (arch=um), add config
check to include lpm levels.

Change-Id: Ia1bd51da4952e56b945a5e51a3b1ff8aaa643cd5
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>