media: cec: rename pin events/function

The CEC_EVENT_PIN_LOW/HIGH defines and the cec_queue_pin_event() function
did not specify that these were about CEC pin events.

Since in the future there will also be HPD pin events it is wise to rename
the event defines and function to CEC_EVENT_PIN_CEC_LOW/HIGH and
cec_queue_pin_cec_event() now before these become part of the ABI.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>