platform: arm64: thinkpad-t14s-ec: add suspend handler for keyboard backlight

This ensures that the keyboard backlight state is restored after
a suspend-resume cycle. Otherwise the keyboard is automatically
disabled during suspend and then stays disabled after resume.

Note, that this adopts the same behavior as the existing Thinkpad
ACPI driver.

Signed-off-by: Sebastian Reichel <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Reviewed-by: Ilpo Järvinen <[e-mail]>
Signed-off-by: Ilpo Järvinen <[e-mail]>

drivers/platform/arm64/lenovo-thinkpad-t14s.c

···
 {
 	struct t14s_ec *ec = dev_get_drvdata(dev);
 
+	led_classdev_suspend(&ec->kbd_backlight);
+
 	t14s_ec_write_sequence(ec, T14S_EC_REG_MODERN_STANDBY,
 			       T14S_EC_MODERN_STANDBY_ENTRY, 3);
 
···
 
 	t14s_ec_write_sequence(ec, T14S_EC_REG_MODERN_STANDBY,
 			       T14S_EC_MODERN_STANDBY_EXIT, 3);
+
+	led_classdev_resume(&ec->kbd_backlight);
 
 	return 0;
 }