mb/google/brox/lotso: Add Fn key scancode

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

BUG=b:322721490
TEST=Flash Lotso, boot to Linux kernel, and verify that KEY_FN is
generated when pressed using `evtest`.

Change-Id: I999627f0ea9db1d79376150a04920ac877a48447
Signed-off-by: Wen Zhang <zhangwen6@huaqin.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83204
Reviewed-by: Dengwu Yu <yudengwu@huaqin.corp-partner.google.com>
Reviewed-by: Varshit Pandya <pandyavarshit@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/mainboard/google/brox/Kconfig

@@ -1,5 +1,8 @@
 ## SPDX-License-Identifier: GPL-2.0-only
 
+config ACPI_FNKEY_GEN_SCANCODE
+	default 94 if BOARD_GOOGLE_LOTSO
+
 config BOARD_GOOGLE_BROX_COMMON
 	def_bool n
 	select DRIVERS_GENERIC_GPIO_KEYS