mb/google/volteer: Enable PCIEXP_HOTPLUG for TCSS TBT/USB4 ports

This change enables PCIEXP_HOTPLUG to support resource allocation for
TCSS TBT/USB4 ports.

BUG=b:149186922

Signed-off-by: Furquan Shaikh <furquan@google.com>
Change-Id: I4cb820e83da40434b00198b934453805e35ef1ab
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41156
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/mainboard/google/volteer/Kconfig b/src/mainboard/google/volteer/Kconfig
index de77633..6875963 100644
--- a/src/mainboard/google/volteer/Kconfig
+++ b/src/mainboard/google/volteer/Kconfig
@@ -15,6 +15,7 @@
 	select MAINBOARD_HAS_CHROMEOS
 	select MAINBOARD_HAS_SPI_TPM_CR50
 	select MAINBOARD_HAS_TPM2
+	select PCIEXP_HOTPLUG
 	select SOC_INTEL_TIGERLAKE
 
 if BOARD_GOOGLE_BASEBOARD_VOLTEER
@@ -66,6 +67,20 @@
 	int
 	default 8
 
+# Reserving resources for PCIe Hotplug as per TGL BIOS Spec (doc #611569)
+# Revision 0.7.6 Section 7.2.5.1.5
+config PCIEXP_HOTPLUG_BUSES
+	int
+	default 42
+
+config PCIEXP_HOTPLUG_MEM
+	hex
+	default 0xc200000  # 194 MiB
+
+config PCIEXP_HOTPLUG_PREFETCH_MEM
+	hex
+	default 0x1c000000 # 448 MiB
+
 config TPM_TIS_ACPI_INTERRUPT
 	int
 	default 21  # GPE0_DW0_21 (GPP_C21)