mb/emul/qemu-q35: Add a _DIS method for gsi_link devices

This solves the remark:
```
dsdt.asl    430-437:   Device(GSIA-H) { Name(_HID, EISAID("PNP0C0F")) Name(_UID, 0) Name(_PRS, ResourceTemplate() { Interrupt(, Level, ActiveHigh, Shared) { 0x17 } }) Name(_CRS, ResourceTemplate() { Interrupt(, Level, ActiveHigh, Shared) { 0x17 } }) Method(_SRS, 1, NotSerialized
[*** iASL: Very long input line, message below refers to column 13 ***]
Remark   2141 -    Missing dependency (Device has a _SRS, no corresponding _DIS)
```

Change-Id: I5c30ed8e7eef324373c3cec6bf16ddcc056c055b
Signed-off-by: Evie (Ivi) Ballou <iviballou@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/91034
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/emulation/qemu-q35/dsdt.asl

@@ -350,6 +350,8 @@ DefinitionBlock (
 			})                                                  \
 			Method(_SRS, 1, NotSerialized) {                    \
 			}                                                   \
+			Method(_DIS, 0, NotSerialized) {                    \
+			}                                                   \
 		}
 
 		define_gsi_link(GSIA, 0, 0x10)