tests/drmdevices: install alongside other utilities

It's mildly useful program, to ship it when the user wants the "tests"
installed. Obviously the "tests" in the name is a misnomer.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Tested-by: Robert Foss <robert.foss@collabora.com>
Reviewed-by: Robert Foss <robert.foss@collabora.com>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>