mb/google/brya/var/mithrax: update overridetree and Kconfig

1. Update override devicetree based on schematics.
2. Update Kconfig based on schematics.

BUG=b:229191897
TEST=emerge-brya coreboot chromeos-bootimage

Signed-off-by: John Su <john_su@compal.corp-partner.google.com>
Change-Id: Ia28ae16f609fda6d90558e69b2d41139dbe533fd
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64329
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Frank Wu <frank_wu@compal.corp-partner.google.com>
diff --git a/src/mainboard/google/brya/Kconfig b/src/mainboard/google/brya/Kconfig
index c8c2911..9bc07c4 100644
--- a/src/mainboard/google/brya/Kconfig
+++ b/src/mainboard/google/brya/Kconfig
@@ -122,6 +122,7 @@
 	default 0x1 if BOARD_GOOGLE_CROTA
 	default 0x1 if BOARD_GOOGLE_MOLI
 	default 0x1 if BOARD_GOOGLE_OSIRIS
+	default 0x1 if BOARD_GOOGLE_MITHRAX
 
 config DRIVER_TPM_I2C_ADDR
 	hex