ARM: add support for the EET board, based on the i.MX31 pcm037 module

The "EET" variant of the pcm037 board has an OLED display, using a S6E63D6
display controller on the first SPI interface, using GPIO57 as a chip-select
for it. S6E63D6 is initialised in the boot-loader, so we only have to take care
of the LCD. EET also adds several buttons and LEDs on GPIOs. This patch adds a
"pcm037_variant=" kernel command line parameter to specify at boot-time which
board the kernel is running on, default is "pcm970", specify "eet" for the EET
board.

Signed-off-by: Guennadi Liakhovetski <lg@denx.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>