platform/x86: acer-wmi: add automatic keyboard background light toggle key as KEY_LIGHTS_TOGGLE

Got a dmesg message on my AMD Renoir based Acer laptop:
"acer_wmi: Unknown key number - 0x84" when toggling keyboard
background light
Signed-off-by: Timo Witte <timo.witte@gmail.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
Link: https://lore.kernel.org/r/20200804001423.36778-1-timo.witte@gmail.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/acer-wmi.c

@@ -111,6 +111,7 @@ static const struct key_entry acer_wmi_keymap[] __initconst = {
 	{KE_KEY, 0x64, {KEY_SWITCHVIDEOMODE} },	/* Display Switch */
 	{KE_IGNORE, 0x81, {KEY_SLEEP} },
 	{KE_KEY, 0x82, {KEY_TOUCHPAD_TOGGLE} },	/* Touch Pad Toggle */
+	{KE_IGNORE, 0x84, {KEY_KBDILLUMTOGGLE} }, /* Automatic Keyboard background light toggle */
 	{KE_KEY, KEY_TOUCHPAD_ON, {KEY_TOUCHPAD_ON} },
 	{KE_KEY, KEY_TOUCHPAD_OFF, {KEY_TOUCHPAD_OFF} },
 	{KE_IGNORE, 0x83, {KEY_TOUCHPAD_TOGGLE} },