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

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

DSPBridge also uses the clockdomain headers for some reason, so,
modify it also. The DSPBridge code should not be including the
clockdomain 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>
Tested-by: Rajendra Nayak <rnayak@ti.com>
Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>