sh-pfc: sh73a0: Add VCCQ MC0 regulator

The sh73a0 has an internal power gate on the VCCQ power supply for the
SDHI0 device that is controlled (for some strange reason) by a bit in a
PFC register. This feature should be exposed as a regulator.

As the same register is also used for pin control purposes there is no
way to achieve atomic read/write sequences with a separate regulator
driver. We thus need to implement the regulator here.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>