mb/google/guybrush: enable display backlight in ramstage

Commit c7204b5a4 [mb/google/guybrush: Enable backlight in the OS]
disabled the GPIO for the display backlight in favor of using ACPI
to enable it, but this breaks display output for payloads which do
not/can not enable the backlight GPIO themselves (edk2, grub, SeaBIOS).

Re-enable the GPIO for display backlight so that payloads other than
depthcharge work properly.

TEST=build/boot google/dewatt with Tianocore payload, verify payload
display visible.

Change-Id: I2519d779954ed89486045aa7de0b18f1c31a4374
Signed-off-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67246
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martin.roth@amd.corp-partner.google.com>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

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

@@ -138,7 +138,7 @@ static const struct soc_amd_gpio base_gpio_table[] = {
 	PAD_GPO(GPIO_121, LOW),
 	/* GPIO_122 - GPIO_128: Not available */
 	/* SOC_DISABLE_DISP_BL */
-	PAD_GPO(GPIO_129, HIGH),
+	PAD_GPO(GPIO_129, LOW),
 	/* WLAN_DISABLE */
 	PAD_GPO(GPIO_130, LOW),
 	/* CLK_REQ3_L */