ARM: OMAP: Split clocks.c into plat-omap/clock.c and mach-omap1/clock.c

This patch contains the following changes:

- Move omap1 specific clock code into mach-omap1/clock.c leaving only
  common code shared between omap1 and omap2 to plat-omap/clock.c.

- Move clock.h and sram.h header files to include/asm-arm/arch-omap/

- Change clock init to register omap1 specific functions with
  plat-omap/clock.c

- Some clean-up of code

This patch makes no functional changes to omap1 clocks.