PM / Sleep: Merge internal functions in generic_ops.c

After the change that removed the code related to runtime PM
from __pm_generic_call() and __pm_generic_resume() these two
functions need not be separate any more, so merge them.

Change-Id: I4538ce980c78f4ef0629a867080168e663956164
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>