mb/google/zork: Add UPD xhci0_force_gen1 for Trembyle and Ezkinil

Add UPD xhci0_force_gen1 for Trembyle and Ezkinil.
The default setting is set to disable, and set enabled for Ezkinil.
Trambyle -> set default as disable.
Ezkinil  -> set enable by request.

BUG=b:156314787
BRANCH=trembyle-bringup
TEST=Build. Verified the setting will be applied on Ezkinil/Trembyle.

Signed-off-by: Lucas Chen <lucas.chen@quanta.corp-partner.google.com>
Change-Id: I65d06bfe379f9e42101bfae1a02a619ee2f24052
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/coreboot/+/2216090
Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42217
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-by: Eric Peers <epeers@google.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>

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

@@ -48,6 +48,8 @@ chip soc/amd/picasso
 
 	register "sd_emmc_config" = "SD_EMMC_EMMC_HS400"
 
+	register "xhci0_force_gen1" = "0"
+
 	# SPI Configuration
 	register "common_config.spi_config" = "{
 		.normal_speed = SPI_SPEED_66M, /* MHz */

src/mainboard/google/zork/variants/ezkinil/overridetree.cb

@@ -22,6 +22,8 @@ chip soc/amd/picasso
 
 	# End : OPN Performance Configuration
 
+	register "xhci0_force_gen1" = "1"
+
 	# Enable I2C2 for trackpad, touchscreen, pen at 400kHz
 	register "i2c[2]" = "{
 		.speed = I2C_SPEED_FAST,