mb/google/brya/xol: Add Fn key scancode

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

BUG=b:327656989
TEST=Flash xol, boot to Linux kernel, and verify that KEY_FN is
generated when pressed using `evtest`.

Change-Id: I34ed93d9666504bfd4d439e166911e49f58e5ff5
Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82069
Reviewed-by: Eric Lai <ericllai@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>

src/mainboard/google/brya/Kconfig

@@ -1,5 +1,8 @@
 ## SPDX-License-Identifier: GPL-2.0-only
 
+config ACPI_FNKEY_GEN_SCANCODE
+	default 94 if BOARD_GOOGLE_XOL
+
 config BOARD_GOOGLE_BRYA_COMMON
 	def_bool n
 	select DRIVERS_GENERIC_ALC1015