Fix remaining sparse warnings in arch/arm/mach-omap2

Fix remaining sparse warnings in arch/arm/mach-omap2/.	These fixes
mostly consist of:

- tagging appropriate integer<->pointer casts with __force

- marking private structures and functions as static; adding function
  prototypes in .h files for public functions

- assigning NULL to pointers, not 0

- adding prototypes for *_init() functions in the appropriate header
  files, and getting rid of the corresponding open-coded extern
  prototypes in other C files

Also clean up checkpatch issues - this mostly involves converting some
asm/ includes to linux/ includes.

While here, shrink some bitfields in struct omap_pwm_led_platform_data
down to the smallest possible type.

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