mainboard/google/kahlee: Set EMMC reset pin to output low

While the pin was set to a pull-down, with the external pull-up, this
wasn't enough to keep the pin low.  Set to output low to drive to 0V.

TEST=Boot grunt, verify EMMC_BRIDGE_RST is 0V.
BUG=b:115661061

Change-Id: Ife014b8a879274df5d892c1de386976808de1df0
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/28649
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/mainboard/google/kahlee/variants/baseboard/gpio.c

@@ -54,7 +54,7 @@ static const struct soc_amd_gpio gpio_set_stage_reset[] = {
 	PAD_NF(GPIO_26, PCIE_RST_L, PULL_NONE),
 
 	/* GPIO_40 - EMMC_BRIDGE_RST */
-	PAD_GPI(GPIO_40, PULL_DOWN),
+	PAD_GPO(GPIO_40, LOW),
 
 	/* GPIO_70 - WLAN_PE_RST_L */
 	PAD_GPO(GPIO_70, HIGH),