mb/google/guybrush: Set eSPI alert as dedicated open drain

Guybrush based boards must usa a dedicated eSPI alert#.
Must be open drain to prevent power leaks.
Keep guybrush reference board in-band since alert# may not be connected.

BUG=b:198409370
TEST=Build guybrush and nipperkin, boot guybrush
BRANCH=None

Change-Id: I4b23bfc6a1167aebfde5acd524fda043b63163dc
Signed-off-by: Rob Barnes <robbarnes@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57313
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/mainboard/google/guybrush/variants/baseboard/devicetree.cb

@@ -36,7 +36,7 @@ chip soc/amd/cezanne
 		.io_mode = ESPI_IO_MODE_QUAD,
 		.op_freq_mhz = ESPI_OP_FREQ_33_MHZ,
 		.crc_check_enable = 1,
-		.alert_pin = ESPI_ALERT_PIN_IN_BAND,
+		.alert_pin = ESPI_ALERT_PIN_OPEN_DRAIN,
 		.periph_ch_en = 1,
 		.vw_ch_en = 1,
 		.oob_ch_en = 0,

src/mainboard/google/guybrush/variants/guybrush/overridetree.cb

@@ -168,4 +168,7 @@ chip soc/amd/cezanne
 		end
 	end
 
+	# TODO(b/198596430): Disable in-band alerts after majority boards are reworked
+	register "common_config.espi_config.alert_pin" = "ESPI_ALERT_PIN_IN_BAND"
+
 end	# chip soc/amd/cezanne