Camera: Clarify camera2 id usage when retrieving camcorder profiles

Clarify that camera2 ids can be used to query camcorder profiles as
long as the devices are capable of producing color output and are not
external.

Bug: 168527175
Test: make docs & check generated doc output.
Change-Id: Idf4bd3e71577b4fc72a164a2fe77caafdbd293ed