ARM: OMAP2: Powerdomain: Add OMAP2/3 common powerdomains

Add powerdomains common to both OMAP2 and OMAP3 (WKUP and GFX/SGX).
Modify mach-omap2/io.c to initialize the powerdomain code on boot.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>