ARM: OMAP: Introduce omap_globals and prcm access functions for multi-omap

New struct omap_globals contains the omap processor specific
module bases. Use omap_globals to set the various base addresses
to make detecting omap chip type simpler.

Also introduce OMAP1_IO_ADDRESS and OMAP2_IO_ADDRESS for future multi-omap
patches.

Signed-off-by: Tony Lindgren <tony@atomide.com>