mb/google/rex: add Elan HID over SPI ASL for Rex0

This patch enables adding variant specific ASL code

TEST=Kernel driver is able to communicate with device

Signed-off-by: Eran Mitrani <mitrani@google.com>
Change-Id: I231482d56dd4afa150766c07cfde105158e5e124
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74886
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>

src/mainboard/google/rex/dsdt.asl

@@ -37,4 +37,11 @@ DefinitionBlock(
 		/* ACPI code for EC functions */
 		#include <ec/google/chromeec/acpi/ec.asl>
 	}
+	/* Mainboard specific */
+#if CONFIG(BOARD_GOOGLE_REX0)
+	Scope (\_SB.PCI0.SPI0)
+	{
+		#include <variant/acpi/hid_spi_elan.asl>
+	}
+#endif
 }