[ARM] pxa: mmc: add 2nd host controller support for pxa3xx

This patch is to add the second mmc controller support for pxa3xx.
It's valid for pxa3[0|1|2]0.

On zylonite, the second controller has no slot.

Signed-off-by: Bridge Wu <bridge.wu@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>