OMAP: smartreflex: move plat/smartreflex.h to mach-omap2/smartreflex.h

There's no reason for this header file to be in
plat-omap/include/plat/smartreflex.h.  The hardware devices are in
OMAP2+ SoCs only.  Leaving this header file in plat-omap causes
problems due to cross-dependencies with other header files that should
live in mach-omap2/.

Thanks to Benoît Cousson <b-cousson@ti.com> for suggesting the removal
of the smartreflex.h include from the OMAP3xxx hwmod data.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Benoît Cousson <b-cousson@ti.com>