reset: uniphier: add reset controller driver for UniPhier SoCs

This is the initial commit for UniPhier reset controller driver.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>