MMC for PXA 27X (resubmit)

MMC support for X_Scale PXA is broken and does not work.
Mainly, the mmc_init() function cannot recognize current SD/MMC cards.
There were already some patches around the world but none of them was
merged into the official u-boot tree.

This patch makes order fixing this issue. Resubmit after code cleanup.

Applied and tested on PXA 270 (TrizepsIV module).

Signed-off-by: Stefano Babic <sbabic@denx.de>