drm/plane-helper: Use proper plane init function

drm/plane-helper: Use proper plane init function

drm_plane_init() (the legacy plane initialization function) takes a bool
as its final parameter; originally this indicated whether a plane was
'private' to the driver (before the DRM core understood non-overlay
planes), now it indicates whether the plane is a primary plane (private
planes were used by some drivers to represent primary planes
internally).  The newer drm_universal_plane_init() take an 'enum
drm_plane_type' as its final parameter to allow the caller to specify
the specific plane type desired (primary, cursor, or overlay).

Due to a rebasing mistake, the primary plane helper is currently passing
DRM_PLANE_TYPE_PRIMARY (enum value = 1) for drm_plane_init()'s boolean
'is_primary' parameter.  This winds up giving the correct behavior since
DRM_PLANE_TYPE_PRIMARY evaluates as true, but is confusing to anyone
reading the code since we're passing an enum value (one of three
possible values) for a boolean parameter.

Replace the primary plane helper's call to drm_plane_init() with
drm_universal_plane_init() so that the parameter and value types match
up as expected.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>