mb/google/myst: Enable mp2 device

The mp2 PCI device is still present when no mp2 firmware is loaded. When
this device isn't explicitly enabled in the mainboard's devicetree, the
chipset devicetree default of the device being disabled is used. This
results in coreboot's resource allocator not allocating resources to
the device and since the bridge doesn't have enough MMIO space reserved,
the Linux kernel can't assign resources to it. Enable the mp2 device in
the mainboard's devicetree so that it gets its resources assigned by
coreboot.

BUG=b:277217097
TEST=builds

Change-Id: I21885c51ff08846b456675090946f381843ef5e6
Signed-off-by: Jon Murphy <jpmurphy@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74277
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/myst/variants/baseboard/devicetree.cb

@@ -132,6 +132,7 @@ chip soc/amd/phoenix
 				end
 			end
 			device ref acp on end # Audio Processor (ACP)
+			device ref mp2 on end # Sensor Fusion Hub (MP2)
 		end
 		device ref gpp_bridge_c on  # Internal GPP Bridge 2 to Bus C
 			device ref usb4_xhci_0 on