google/oak: dsi: set mipi pin driving control on

We set this driving control to prevent signal attenuation caused by
LVDS DRV termination.

When DA_LVDSTX_PWR_ON is not set, LVSH has no power and LVDS DRV
termination status is unknown(floating). This creates a chance that MIPI
output would be influenced. The DSI's LP signal will be half voltage
attenuation. There will be no display on panel.

When DA_LVDSTX_PWR_ON is set, LVSH and LVDS DRV termination are
effective and termination is fixed OFF. The DSI won't be influenced.

We only need to set this register once, so we set it here to prevent
repeat setting in the kernel when the system goes to recovery mode.

BUG=chrome-os-partner:55296
BRANCH=none
TEST=build pass elm and show ui

The original commit in the cros repo combined the chipset and mainboard
code changes.  This has been split for the push to coreboot.org

Change-Id: I733bdd115950b71493856220414ac0dd75d28122
Signed-off-by: Martin Roth <martinroth@chromium.org>
Original-Commit-Id: 0d25a27f300acc4b65a894110d3ee0cc9676cd12
Original-Change-Id: Ie71f9cc41924787be8539c576392034320b57a49
Original-Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/360850
Original-Commit-Ready: jitao shi <jitao.shi@mediatek.com>
Original-Tested-by: jitao shi <jitao.shi@mediatek.com>
Original-Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/15808
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/google/oak/mainboard.c

@@ -252,6 +252,10 @@ static void mainboard_init(device_t dev)
 	gpio_input(PAD_EINT1); /* SD_DET */
 
 	configure_audio();
+
+	/* fix dsi lp mode is half voltage attenuation */
+	mtk_dsi_pin_drv_ctrl();
+
 	if (display_init_required()) {
 		configure_backlight();
 		configure_display();