rk3399: syscon: add support for pmugrf

pmugrf is a module like grf which contain some of the iomux registers
and other registers.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>

arch/arm/include/asm/arch-rockchip/clock.h

@@ -16,6 +16,7 @@ enum {
 	ROCKCHIP_SYSCON_GRF,
 	ROCKCHIP_SYSCON_SGRF,
 	ROCKCHIP_SYSCON_PMU,
+	ROCKCHIP_SYSCON_PMUGRF,
 };
 
 /* Standard Rockchip clock numbers */