power: qcom: apm: correct various coding style issues

Correct warnings flagged by checkpatch.  In particular, modify
the following:

 - Use octal file permissions instead of symbolic.

 - Add 'const' to type of struct of_device_id variable.

 - Remove unnecessary out-of-memory error message.

 - Update the the MSM_APM Kconfig entry.

Change-Id: I57c6d499c90db62ca2733f302bd045b4d439905f
Signed-off-by: David Collins <collinsd@codeaurora.org>