platform/x86: dell-wmi: Ignore keyboard attached / detached events

Ignore events with a type of 0x0011 and a code of 0xfff2 / 0xfff3,
this silences the following messages being logged when the keyboard is
detached / attached on a Dell Venue 11 Pro 7130:

[   63.621953] dell_wmi: Unknown key with type 0x0011 and code 0xfff2 pressed
[   70.240558] dell_wmi: Unknown key with type 0x0011 and code 0xfff3 pressed

Note SW_TABLET_MODE is already reported through the intel_vbtn driver on
this and other Dell devices, so dell_wmi should not report this too,
to avoid duplicate events.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Mario Limonciello <Mario.limonciello@dell.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>