mb/google/rex: enable d3hot for storage devices

_DSD "StorageD3Enable" property is needs to be set under the root
port in the DSDT or SSDT. The ACPI _DSD method is the preferred way
to opt D3hot support for storage devices.

This also bypasses the low LTR from SSD that blocking S0i2.2
LTR/latency SoC requirement.

Name (_DSD, Package () {
    ToUUID("5025030F-842F-4AB4-A561-99A5189762D0"),
        Package () {
            Package (2) {"StorageD3Enable", 1},
            // 1 - Enable; 0 - Disable
        }
    }
)

BUG=b:289028958
TEST=Check code compiles & boot rex, and verify the "StorageD3Enable"
SSDT entry.

Change-Id: I19decc2706954e73bc28fc2d9c3c4d18d2c384b7
Signed-off-by: Kangheui Won <khwon@chromium.org>
Signed-off-by: Sukumar Ghorai <sukumar.ghorai@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76835
Reviewed-by: Sumeet R Pawnikar <sumeet.r.pawnikar@intel.com>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/rex/variants/rex0/overridetree.cb

@@ -303,6 +303,13 @@ chip soc/intel/meteorlake
 				.clk_req = 4,
 				.flags = PCIE_RP_LTR | PCIE_RP_AER,
 			}"
+			chip soc/intel/common/block/pcie/rtd3
+				register "is_storage" = "true"
+				register "enable_gpio" = "ACPI_GPIO_OUTPUT_ACTIVE_HIGH(GPP_A19)"
+				register "reset_gpio" = "ACPI_GPIO_OUTPUT_ACTIVE_LOW(GPP_A20)"
+				register "srcclk_pin" = "4"
+				device generic 0 on end
+			end
 		end	#PCIE9 SSD card
 		device ref ish on
 			probe ISH ISH_ENABLE