ARM: Rockchip: add power domain drivers for Rockchip

Add basic support for generic power domain for Rockchip platform
and add pd_gpu in rk3288 as example.

Signed-off-by: dkl <dkl@rock-chips.com>
Signed-off-by: Caesar Wang <caesar.wang@rock-chips.com>

Change-Id: Ib99e53541a0072a058d4a56e641b0b784e3709cc
dt-bindings: add document Rockchip Power domain

Signed-off-by: dkl <dkl@rock-chips.com>
Signed-off-by: Caesar Wang <caesar.wang@rock-chips.com>
Change-Id: I40d7ff328c37a4af63e0727a601a8e8ad851f446
ARM: dts: Add Power domain DT node for RK3288 Soc

Signed-off-by: Caesar Wang <caesar.wang@rock-chips.com>
Change-Id: Ib48f96cf3e0ab7be56dae125c114aefc1afad654