drm/omap: Add PM capabilities

Added power management capabilities into the omapdrm and DMM drivers.
During suspend, we don't need to do anything to maintain the state of
the LUT.  We have all the necessary information to recreate the mappings
of the GEM object list maintained by the omapdrm driver.

On resume, the DMM resume handler will first reprogram the LUT to point
to the dummy page.  The subsequent resume handler in the omapdrm will call
into the DMM and reprogram each of the buffer objects.  This will ensure
that all of the necessary objects will be pinned into the DMM properly.

Order of suspend/resume handlers is done by device creation.  We create
the DMM device before the omapdrm, so the correct order is maintained.

Signed-off-by: Andy Gross <andy.gross@ti.com>
Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>