fbdev: omap: avoid using mach/*.h files

All the headers we actually need are now in include/linux/soc,
so use those versions instead and allow compile-testing on
other architectures.

Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>