i.mx: i.mx6q: add the initial support for i.mx6q ARM2 board

i.mx: i.mx6q: add the initial support for i.mx6q ARM2 board

Add the initial support for Freescale i.MX6Q Armadillo2 board
Support: MMC boot from slot 0/1, debug UART(UART4), usdhc.

There is two MMC slots on the boards:
mmc dev 0 -> connect USDHC3 -> the lower slot on the board,
mmc dev 1 -> connect USDHC4 -> the upper slot on the board,

Signed-off-by: Jason Liu <jason.hui@linaro.org>
Cc: Stefano Babic <sbabic@denx.de>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>