ARM: dts: alt: add SDHI0 and 1 support

Define the Alt board dependent part of the SDHI0 and 1
device nodes along with the necessary voltage regulators.

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

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