OMAP: PM constraints: add return values; add requesting device param to omap_pm_set_max_dev_wakeup_lat()

Add return values to the PM constraint functions.  This allows the PM
core to provide feedback to the caller if a constraint is not
possible.  Update the one upstream user of omap_pm_set_max_mpu_wakeup_lat()
to add a compatibility wrapper, needed until the driver is changed.

Update some of the documentation to conform more closely to kerneldoc style.

Add an additional device parameter to omap_pm_set_max_dev_wakeup_lat()
to identify the device requesting the constraint.  This is so repeated calls
to omap_pm_set_max_dev_wakeup_lat() with the same requesting device can
override the device's previously-set constraint.  Also, it allows the PM
core to make a decision as to whether or not the constraint should be
satisfied, based on the caller's identity.
Signed-off-by: Paul Walmsley <paul@pwsan.com>