HID: wiimote: Add drm request

The wiimote reports data in several data reporting modes (DRM). The DRM
request makes the wiimote send data in the requested drm.

The DRM mode can be set explicitely or can be chosen by the driver. To let
the driver choose the DRM mode, pass WIIPROTO_REQ_NULL placeholder to it. This
is no valid request and is replaced with an appropriate DRM.

Currently, the driver always sets the basic DRM_K mode, but this will be
extended when further peripherals like accelerometer and IR are supported.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>