sio/ite/it8783ef: Return (0) in ACPI _PSC methods

Current ACPI code for UARTs uses the PNP_DEFAULT_PSC macro for _PSC
(current power state) methods. Override it to `Return (0)` (i.e. cur-
rent state is D0) as the IT8783E/F doesn't have power management.

Change-Id: I3c858dde287dbf7e5fc0c20abb1fd374887acdde
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/17791
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/superio/ite/it8783ef/acpi/superio.asl

@@ -51,6 +51,9 @@
 #define SUPERIO_CHIP_NAME IT8783EF
 #include <superio/acpi/pnp.asl>
 
+#undef PNP_DEFAULT_PSC
+#define PNP_DEFAULT_PSC Return (0) /* no power management */
+
 #define CONFIGURE_CONTROL CCTL
 
 Device(SUPERIO_DEV) {