drm/atomic: Allow for holes in connector state, v2.

Because we record connector_mask using 1 << drm_connector_index now
the connector_mask should stay the same even when other connectors
are removed. This was not the case with MST, in that case when removing
a connector all other connectors may change their index.

This is fixed by waiting until the first get_connector_state to allocate
connector_state, and force reallocation when state is too small.

As a side effect connector arrays no longer have to be preallocated,
and can be allocated on first use which means a less allocations in
the page flip only path.

Changes since v1:
- Whitespace. (Ville)
- Call ida_remove when destroying the connector. (Ville)
- u32 alloc -> int. (Ville)

Fixes: 14de6c44 ("drm/atomic: Remove drm_atomic_connectors_for_crtc.")
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Lyude <cpaul@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>