soc/intel/tgl,mb/google/volteer: Add API for Type-C aux bias pads

TGL boards using the Type-C subsystem for USB Type-C ports without a
retimer attached may require a DC bias on the aux lines for certain
modes to work. This patch adds native coreboot support for programming
the IOM to handle this DC bias via a simple devicetree
setting. Previously a UPD was required to tell the FSP which GPIOs were
used for the pullup and pulldown biases, but the API for this UPD was
effectively undocumented.

BUG=b:174116646
TEST=Verified on volteer2 that a Type-C flash drive is enumerated
succesfully on all ports. Verified all major power flows (boot, reboot,
powerdown and S0ix/suspend) still work as expected.

Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Change-Id: I70e36a41e760f4a435511c147cc5744a77dbccc0
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51649
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
diff --git a/src/mainboard/google/volteer/variants/malefor/overridetree.cb b/src/mainboard/google/volteer/variants/malefor/overridetree.cb
index 00d609f..0d25df8 100644
--- a/src/mainboard/google/volteer/variants/malefor/overridetree.cb
+++ b/src/mainboard/google/volteer/variants/malefor/overridetree.cb
@@ -12,8 +12,7 @@
 	register "SaGv" = "SaGv_Disabled"
 
 	register "TcssAuxOri" = "1"
-	register "IomTypeCPortPadCfg[0]" = "0x090E000A"
-	register "IomTypeCPortPadCfg[1]" = "0x090E000D"
+	register "typec_aux_bias_pads[0]" = "{.pad_auxp_dc = GPP_E10, .pad_auxn_dc = GPP_E13}"
 
 	# I2C Port Config
 	register "SerialIoI2cMode" = "{