ARM: dts: alt: add MMCIF support

Define the Alt board dependent part of the MMCIF device node.

Like the Silk the board has eMMC chip along with the  necessary voltage
regulator (note that the Vcc/Vccq regulator is dummy -- it's required by
the MMCIF driver but doesn't actually exist on the board).

Based on work for the Silk board by Vladimir Barinov and Sergei Shtylyov.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>