rockchip/rk3399: Moving romstage.c to mainboard/gru

The romstage.c is more board related than soc specific, like
setting the pwm regulators, so moving it to mainboard/gru.

BRANCH=none
BUG=chrome-os-partner:54819
TEST=Bootup on kevin board

Change-Id: If2bf245302eb4fb20bb089c1b3ffa03909722443
Signed-off-by: Shunqian Zheng <zhengsq@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/375398
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/mainboard/google/gru/Makefile.inc

@@ -24,6 +24,7 @@ verstage-y += reset.c
 romstage-y += boardid.c
 romstage-y += chromeos.c
 romstage-y += memlayout.ld
+romstage-y += romstage.c
 romstage-y += sdram_configs.c
 
 ramstage-y += boardid.c

src/soc/rockchip/rk3399/Makefile.inc

@@ -49,7 +49,6 @@ romstage-y += clock.c
 romstage-y += mmu_operations.c
 romstage-y += ../common/pwm.c
 romstage-y += timer.c
-romstage-y += romstage.c
 romstage-y += tsadc.c
 romstage-y += usb.c
 romstage-y += gpio.c