Camera: Support TEST_PATTERN_MODE_BLACK for camera muting

If test pattern mode BLACK is supported, but SOLID_COLOR is not,
use it for implementing camera muting.

Also fix up incorrect docs for test patterns

Test: Camera CTS continues to pass
Bug: 189507251
Change-Id: I3db57f42c5615bba28f1b59e61adcde1d0640590
3 files changed