media: cec-pin-error-inj: parse/show error injection

Add support to the CEC Pin framework to parse error injection commands
and to show them.

The next patch will do the actual implementation of this.

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