soc/amd/picasso/acpi: Move _PIC method to root namespace

The _PIC method sets the interrupt model (PIC or APIC). It needs to be
defined at the root level for the kernel to find it. Previously this
method was never getting called, so we were always stuck in APIC mode.

BUG=b:139429446, b:147042464
BRANCH=none
TEST=Saw the method getting called
[    1.251774] ACPI Debug:  "PIC MODE: 0000000000000001"

Change-Id: Idd5e9646df8d56e7cbec2be8b4016c36d81e5fb8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/coreboot/+/2095682
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41437
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/soc/amd/picasso/acpi/pci_int.asl

@@ -103,12 +103,13 @@
 		P3PR, 1,
 	}
 
-	Method(_PIC, 0x01, NotSerialized)
+	Method(\_PIC, 0x01, NotSerialized)
 	{
 		If (Arg0)
 		{
 			\_SB.CIRQ()
 		}
+		printf("PIC MODE: %o", Arg0)
 		Store(Arg0, PMOD)
 	}