ARM: OMAP: remove plat/clock.h

Remove arch/arm/plat-omap/include/plat/clock.h by merging it into
arch/arm/mach-omap1/clock.h and arch/arm/mach-omap2/clock.h.
The goal here is to facilitate ARM single image kernels by removing
includes via the "plat/" symlink.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
[tony@atomide.com: fixed to remove duplicate clock.h includes]
Signed-off-by: Tony Lindgren <tony@atomide.com>