HID: elecom: add support for ELECOM M-DT2DRBK

The DT2DRBK trackball has 8 buttons, but the report descriptor only
specifies 5. This patch adds the device ID and performs a similar fixup as
for other ELECOM devices to enable the remaining 3 buttons.

Signed-off-by: Martin Hilgendorf <martin.hilgendorf@posteo.de>
Signed-off-by: Jiri Kosina <jkosina@suse.com>