pxamci: add regulator support.

Changes pxamci.c to use the regulator subsystem. Uses the regulator case
CONFIG_REGULATOR is defined and a matching is regulator is provided, or
falls back to pdata->setpower otherwise. A warning is displayed case
both a valid regulator and pdata is set, and the regulator is used.

Signed-off-by: Daniel Ribeiro <drwyrm@gmail.com>
Acked-by: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>