mb/google/brya: Use FW_CONFIG LTE_PCIE to turn on/off the PCIE6

PCIE6 only needed when use the PCIE LTE.

BUG=b:180166408
BRANCH=none
TEST=FM350 can/can't be detected when enable/disable this config.

Signed-off-by: Eric Lai <ericr_lai@compal.corp-partner.google.com>
Change-Id: I9dce05fdb6eb956a054d3815ff706b94f0d3fc37
Reviewed-on: https://review.coreboot.org/c/coreboot/+/54173
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/mainboard/google/brya/variants/brya0/overridetree.cb

@@ -122,6 +122,9 @@ chip soc/intel/alderlake
 				device generic 0 on end
 			end
 		end
+		device ref pcie_rp6 on
+			probe DB_LTE LTE_PCIE
+		end
 		device ref pcie_rp8 on
 			chip soc/intel/common/block/pcie/rtd3
 				register "enable_gpio" = "ACPI_GPIO_OUTPUT_ACTIVE_HIGH(GPP_H13)"