lcd: add corgibl_limit_intensity() to corgi_lcd

This is not generic enough, added here for backward compatibility.
And make this an individual commit so future revert will be a bit
easier.

Signed-off-by: Eric Miao <eric.miao@marvell.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>