mb/google/myst: Enable audio co-processor in devicetree

Enable the audio co-processor in the device tree.

BUG=b:277214614
TEST=builds

Signed-off-by: Jon Murphy <jpmurphy@google.com>
Change-Id: I1e1749359804960bbd75d869385b9071e7f33be7
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74276
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

@@ -131,6 +131,7 @@ chip soc/amd/phoenix
 					end
 				end
 			end
+			device ref acp on end # Audio Processor (ACP)
 		end
 		device ref gpp_bridge_c on  # Internal GPP Bridge 2 to Bus C
 			device ref usb4_xhci_0 on