mb/google/skywalker: Configure GPIO GPIO_AP_EDP_BKLTEN as output

Config GPIO GPIO_AP_EDP_BKLTEN as output low. When skipping firmware
display, it can prevent leakage to GPIO_AP_EDP_BKLTEN and cause it
to be pulled up to a 0.6 V step.

BUG=b:438353560
BRANCH=none
TEST=skip fw display check GPIO_AP_EDP_BKLTEN Waveform

Change-Id: Icea1e035d62c89ea26bc58afa1d64ab8a448cc04
Signed-off-by: Cong Yang <yangcong5@huaqin.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/88772
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yidi Lin <yidilin@google.com>
Reviewed-by: Haikun Zhou <zhouhaikun5@huaqin.corp-partner.google.com>

src/mainboard/google/skywalker/chromeos.c

@@ -33,6 +33,7 @@ void setup_chromeos_gpios(void)
 	gpio_output(GPIO_EN_PWR_FP, 0);
 	gpio_output(GPIO_FP_RST_1V8_S3_L, 0);
 	gpio_output(GPIO_EN_SPKR, 0);
+	gpio_output(GPIO_AP_EDP_BKLTEN, 0);
 }
 
 void fill_lb_gpios(struct lb_gpios *gpios)