platform/x86: dell-wmi: Ignore new rfkill and fn-lock events

There are two new events generated by dell-wmi, rfkill and fn-lock, from
Dell Systems.

When Fn-lock hotkey gets pressed to switch to function mode:
[85951.591542] dell_wmi: Unknown key with type 0x0010 and code 0xe035
pressed
[85951.591546] dell_wmi: Unknown key with type 0x0010 and code 0x0000
pressed

When Fn-lock hotkey gets pressed to switch to multimedia mode:
[85956.667686] dell_wmi: Unknown key with type 0x0010 and code 0xe035
pressed
[85956.667690] dell_wmi: Unknown key with type 0x0010 and code 0x0001
pressed

When radio hotkey gets pressed:
[85974.430220] dell_wmi: Unknown key with type 0x0010 and code 0xe008
pressed

These events are for notification purpose, so we can ignore them.

This patch is tested on XPS 9370.

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