ARM: OMAP2+ Move SoC specific headers to be local to mach-omap2

These can now be moved to be local headers in mach-omap2.

Note that this patch removes arch/arm/plat-omap/devices.c as it
will get removed anyways with Paul Walmsley's patch
"ARM: OMAP: split OMAP1, OMAP2+ RNG device registration".

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