[media] uvcvideo: Remove sysadmin requirements for UVCIOC_CTRL_MAP

This patch removes the sysadmin requirements for UVCIOC_CTRL_MAP (and the stub
implementation of UVCIOC_CTRL_ADD). This requirement no longer makes sense with
the new XU control access mechanisms since XU controls can be accessed without
adding control mappings first.

A maximum number (currently 1024) of control mappings per device is enforced to
avoid excess memory consumption caused by careless user space applications.

Signed-off-by: Martin Rubli <martin_rubli@logitech.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>