ARM: OMAP2+: Drop plat/cpu.h for omap2plus

The cpu_is_omap macros are now local to arch/arm/mach-omap2
in soc.h and plat/cpu.h can finally be dropped for omap2+.
Thanks everybody for help with fixing the drivers.

Note that we can now also remove the unused plat/cpu.h from
smartreflex.c and isp.c as they will cause compile errors
with ARCH_MULTIPLATFORM enabled.

Cc: Kevin Hilman <khilman@deeprootsystems.com>
Acked-by: Jean Pihet <jean.pihet@newoldbits.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>