soc/intel/tigerlake: Update platform.asl to ASL2.0 syntax

This change updates platform.asl to use ASL2.0 syntax. This
increases the readability of the ASL code.

TEST=Verified using --timeless option to abuild that the resulting
coreboot.rom is same as without the ASL2.0 syntax changes for volteer.

Change-Id: I248f5e9a1e3ba4f6426167f0406073252cc6513a
Signed-off-by: V Sowmya <v.sowmya@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42506
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/tigerlake/acpi/platform.asl

@@ -16,5 +16,5 @@
 Method (_PIC, 1)
 {
 	/* Remember the OS' IRQ routing choice. */
-	Store (Arg0, PICM)
+	PICM = Arg0
 }