dell-wmi: Add support for new Dell systems

Newer Dell systems support HotKey features differently from legacy
systems.  A new vendor specifc HotKey SMBIOS table (Type 0xB2) is
defined. This table contains a mapping between scancode and the
corresponding predefined keyfunction ( i.e. keycode).. Also, a new
ACPI-WMI event type (called KeyIDList) with a value of 0x0010 is
defined. Any BIOS containing 0xB2 table will send hotkey notifications
using KeyIDList event.

This is Rezwanul's patch, updated to ensure that brightness events are
not sent if the backlight is controlled via ACPI and with the default
keycode for the display output switching altered to match desktop
expectations.

Signed-off-by: Rezwanul Kabir <Rezwanul_Kabir@dell.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>