ARM: OMAP2+: Remove obsolete Makefile line

The OMAP runtime PM implementation was removed in v3.0. But one Makefile
line, which was used to tweak CFLAGS, was overlooked. Remove it too.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Tony Lindgren <tony@atomide.com>