da850/omap-l138: add callback to control LCD panel power

Add the platform specific callback to control LCD panel and backlight
power.

Signed-off-by: Chaithrika U S <chaithrika@ti.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>