platform/x86: dell-laptop: Fix bogus keyboard backlight sysfs interface

Dell Latitude 3160 does not have keyboard backlight, but there is a
sysfs interface for it, which does nothing at all.

KBD_LED_ON_TOKEN is the only token can be found. Since it doesn't have
KBD_LED_OFF_TOKEN or KBD_LED_AUTO_*_TOKEN, it should be safe to assume
at least two tokens should be present to support keyboard backlight.
Not all models have ON token - they may have multiple AUTO tokens instead.

Models which do not use SMBIOS token to control keyboard backlight, also
have this issue. Brightness level is 0 on these models. Verified on Dell
Inspiron 3565.

Reports keyboard backlight is supported only when at least two modes are
present.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/dell-laptop.c

@@ -1510,7 +1510,11 @@ static void kbd_init(void)
 	ret = kbd_init_info();
 	kbd_init_tokens();
 
-	if (kbd_token_bits != 0 || ret == 0)
+	/*
+	 * Only supports keyboard backlight when it has at least two modes.
+	 */
+	if ((ret == 0 && (kbd_info.levels != 0 || kbd_mode_levels_count >= 2))
+	    || kbd_get_valid_token_counts() >= 2)
 		kbd_led_present = true;
 }