kmstest_get_crtc was skipping because at that point the crtc was not
active yet, instead we should only use igt_assert_plane_visible
directly. Unexport kmstest_get_crtc, since nothing here should need it.
While at it fix a small leak in igt_assert_plane_visible, the only
remaining user.

Additionally, it' s not allowed to obtain crc on a disabled pipe, so
wait until the pipe is enabled before allocating the crc.

Changes since v1:
- Move igt_pipe_crc_new until after pipe is enabled.
- Move test_init() into test_setup(), it's redundant..
- Remove pipe_crc from data, no need to have it there.
Changes since v2:
- Increment fb pointer for igt_plane_set_fb, in order to set a different
  fb on each plane correctly.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>