mmc: uniphier-sd: Add vqmmc regulator support

Add initial support for setting the vqmmc regulator. Since we do not
support 1V8 modes, set the regulator to 3V3 and enable it.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>