superio/nuvoton/nct6776/acpi: Add PS/2 mouse support

By defining SUPERIO_KBC_PS2M, ACPI code is added to show the PS/2 mouse.
This has been tested on an ASUS P8H61-M LX with Linux 4.9.110 and
4.17.8. In each case, the PS/2 mouse works automatically, whereas it was
not detected before.

Change-Id: I7983f85b3fd23547950f1f75a81bbca63c63d52b
Signed-off-by: Tristan Corrick <tristan@corrick.kiwi>
Reviewed-on: https://review.coreboot.org/27797
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/src/superio/nuvoton/nct6776/acpi/superio.asl b/src/superio/nuvoton/nct6776/acpi/superio.asl
index 980eab9..abd5562 100644
--- a/src/superio/nuvoton/nct6776/acpi/superio.asl
+++ b/src/superio/nuvoton/nct6776/acpi/superio.asl
@@ -152,6 +152,7 @@
 	#undef SUPERIO_KBC_PS2M
 	#undef SUPERIO_KBC_PS2LDN
 	#define SUPERIO_KBC_LDN 5
+	#define SUPERIO_KBC_PS2M
 	#include <superio/acpi/pnp_kbc.asl>
 #endif