[ARM] 5094/1: pcm990: Add framebuffer and backlight support

PCM990 boards can be assembled with either a Sharp STN or a NEC TFT LCD. This
patch adds support for these displays and for the backlight, using the pwm_bl
driver.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>