[media] stk1160: Reduce driver verbosity

These messages are not really informational, and just makes the driver's
output too verbose. This commit changes some messages to a debug level,
removes a really useless "driver loaded" message and finally undefines
the DEBUG macro.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>