mb/google/brya/variants/primus: enable PS2 interface

BUG=b:187969783

Signed-off-by: Casper Chang <casper_chang@wistron.corp-partner.google.com>
Change-Id: I1e063524cfa4121c38cfed23e95557953511d884
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56774
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/mainboard/google/brya/variants/primus/include/variant/ec.h

@@ -5,4 +5,7 @@
 
 #include <baseboard/ec.h>
 
+/* Enable PS/2 Mouse */
+#define SIO_EC_ENABLE_PS2M
+
 #endif