ARM: dts: realview: PB1176: define a standard VGA panel

This defines the CLCD block in the PB1176 and adds a standard
640x480 VGA panel to the device tree.

Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>