mmc: esdhc: add support to get voltage from device-tree

Add suppport to get voltage from device-tree node for esdhc host,
if voltage-ranges was specified in device-tree node we can get
ocr_mask instead of read from host capacity register. If not voltages
still can be get from host capacity register.

Signed-off-by: Haijun Zhang <haijun.zhang@freescale.com>
Acked-by: Anton Vorontsov <anton@enomsg.org>
Signed-off-by: Chris Ball <cjb@laptop.org>