Speeds up testcases except for those where we want to exercise the
probing itself. The only exceptions left where we do a full probe are

- pm_rpm: We use it to make sure the kernel doesn't get things wrong
  with power domains, so we really want to exercise the full probe
  paths. And there the only place really is the specific validation
  done with the data gathered by get_drm_info.

- kmstest_force_ functions: Newer kernels should be better at
  re-probing state when the force sysfs fields change, but better safe
  than sorry.

v2: I also consolidated the start_n_modes and start_connectors while
at it - move one of the fixup hunks to this patch that accidentally
got misplaced (Thomas).

Cc: Thomas Wood <thomas.wood@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>