arm, fbdev, omap2, LLVMLinux: Remove nested function from omap2 dss

Replace the use of nested functions where a normal function will suffice.

Nested functions are not liked by upstream kernel developers in general. Their
use breaks the use of clang as a compiler, and doesn't make the code any
better.

This code now works for both gcc and clang.

Signed-off-by: Behan Webster <behanw@converseincode.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>