backlight: ensure platform_lcd on by default

It seems that we need to ensure that the lcd is powered up at start,
otherwise we do not see a display.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>