google/kukui: Enable eMMC in bootblock.

On kukui board, the eMMC is routed to EC for boot ROM emulation when
loading bootblock, and should be set back to real eMMC as early as
possible after bootblock is loaded.

BUG=b:80501386
TEST=make; boots and verified BOOTBLOCK_EN_L GPIO is enabled.
BRANCH=None

Change-Id: Ifefb2e26ed048c38595907cc0875757410129828
Signed-off-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: https://review.coreboot.org/27601
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/kukui/bootblock.c

@@ -14,9 +14,16 @@
  */
 
 #include <bootblock_common.h>
+#include <gpio.h>
+#include <soc/gpio.h>
 #include <soc/spi.h>
 
+#define BOOTBLOCK_EN_L (GPIO(KPROW0))
+
 void bootblock_mainboard_init(void)
 {
+	/* Turn on real eMMC. */
+	gpio_output(BOOTBLOCK_EN_L, 1);
+
 	mtk_spi_init(CONFIG_BOOT_DEVICE_SPI_FLASH_BUS, SPI_PAD0_MASK, 26 * MHz);
 }