SAMv7 encoder driver with GPIO pins was written without IOCTL support.
While this driver does not require any lower level IOCTLs for its
functionality the upper layer fails on assertion when unknown command
can not be send to lower layer. This commit adds IOCTL handler that
always returns -ENOTTY as no commands are supported.
Signed-off-by: Michal Lenc <michallenc@seznam.cz>