mb/google/nissa/var/riven: Add Fn key scancode

The Fn key on riven emits a scancode of 94 (0x5e).

BUG=b:345231373
TEST=Flash riven, boot to Linux kernel, and verify that KEY_FN is
generated when pressed using `evtest`.

Change-Id: Iddedd08fc50e8e8e369ce3d73edf0f3077867e87
Signed-off-by: David Wu <david_wu@quanta.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83614
Reviewed-by: Subrata Banik <subratabanik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Eric Lai <ericllai@google.com>

src/mainboard/google/brya/Kconfig

@@ -1,7 +1,7 @@
 ## SPDX-License-Identifier: GPL-2.0-only
 
 config ACPI_FNKEY_GEN_SCANCODE
-	default 94 if BOARD_GOOGLE_XOL
+	default 94 if (BOARD_GOOGLE_XOL || BOARD_GOOGLE_RIVEN)
 
 config BOARD_GOOGLE_BRYA_COMMON
 	def_bool n