HID: asus: Add support for the ASUS FX503VD laptop

The ASUS FX503VD laptop uses an USB keyboard with several hotkeys
which use the Asus Vendor specific UsagePage.

This uses two usage-codes within the page which have not been seen
before, 0x7c for its mic-mute hotkey and 0x99 for Fn+F5 which has
a "fan" symbol as hotkey symbol on the keyb. we map this to KEY_PROG4
(PROG1-PROG3 are already used).

This commit adds the mappings for the 2 new usage codes and the USB-ids
for this keyboard to the hid-asus driver.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>