mb/supermicro/x11ssh-tf: configure "POST complete" gpio for IPMI driver

Configure the "POST complete" gpio in the devicetree for the BMC/IPMI
driver and set the pad's initial value to 0 since the signal is active-
high and shall be set by the IPMI/BMC driver.

Also add the pad to early gpio config, since it is expected to have an
external pull-up like X11SSM-F, which is wrong and would confuse the BMC.

Test: Boot the machine via the BMC web interface and check that sensors
get read correctly by the IPMI firmware when the payload starts.

Tested successfully.

Change-Id: If344b2271bfc8d50b8b64847109818f96f2abbcb
Tested-by: Patrick Rudolph <siro@das-labor.org>
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48711
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/mainboard/supermicro/x11-lga1151-series/variants/x11ssh-tf/gpio.c

@@ -50,7 +50,7 @@ static const struct pad_config gpio_table[] = {
 	PAD_NC(GPP_B17, NONE),
 	PAD_NC(GPP_B18, NONE),
 	PAD_NC(GPP_B19, NONE),
-	PAD_CFG_GPO(GPP_B20, 1, PLTRST),
+	PAD_CFG_GPO(GPP_B20, 0, PLTRST), /* BMC POST_COMPLETE */
 	PAD_NC(GPP_B21, NONE),
 	PAD_NC(GPP_B22, NONE),
 	PAD_CFG_NF(GPP_B23, NONE, DEEP, NF2),

src/mainboard/supermicro/x11-lga1151-series/variants/x11ssh-tf/gpio_early.c

@@ -14,6 +14,7 @@ static const struct pad_config early_gpio_table[] = {
 	PAD_CFG_NF(GPP_A8, NONE, DEEP, NF1),
 	PAD_CFG_NF(GPP_A9, NONE, DEEP, NF1),
 	PAD_CFG_NF(GPP_A10, NONE, DEEP, NF1),
+	PAD_CFG_GPO(GPP_B20, 0, PLTRST), /* BMC POST_COMPLETE */
 };
 
 void mainboard_configure_early_gpios(void)

src/mainboard/supermicro/x11-lga1151-series/variants/x11ssh-tf/overridetree.cb

@@ -76,6 +76,8 @@ chip soc/intel/skylake
 		end
 		device pci 1f.0 on	# LPC Interface
 			chip drivers/ipmi
+				use pch_gpio as gpio_dev
+				register "post_complete_gpio" = "GPP_B20"
 				# On cold boot it takes a while for the BMC to start the IPMI service
 				register "wait_for_bmc" = "1"
 				register "bmc_boot_timeout" = "60"