ARM: shmobile: kzm9g-reference: Move SDHI regulators to DT

Create two GPIO-controlled fixed-voltage regulators in the
kzm9g-reference DT and remove manual configuration of the corresponding
GPIOs from board code.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>