OMAP2+: powerdomain: move header file from plat-omap to mach-omap2

The OMAP powerdomain code and data is all OMAP2+-specific.  This seems
unlikely to change any time soon.  Move plat-omap/include/plat/powerdomain.h
to mach-omap2/powerdomain.h.  The primary point of doing this is to remove
the temptation for unrelated upper-layer code to access powerdomain code
and data directly.

As part of this process, remove the references to powerdomain data
from the GPIO "driver" and the OMAP PM no-op layer, both in plat-omap.
Change the DSPBridge code to point to the new location for the
powerdomain headers.  The DSPBridge code should not be including the
powerdomain headers; these should be removed.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Omar Ramirez Luna <omar.ramirez@ti.com>
Cc: Felipe Contreras <felipe.contreras@gmail.com>
Cc: Greg Kroah-Hartman <greg@kroah.com>