drm/fb-helper: Apply panel orientation connector prop to the primary plane, v6.

Apply the "panel orientation" drm connector prop to the primary plane so
that fbcon and fbdev using userspace programs display the right way up.

Changes in v3:
-Use a rotation member in struct drm_fb_helper_crtc and set that from
 drm_setup_crtcs instead of looping over all crtc's to find the right one
 later
-Since we now no longer look at rotation quirks directly in the fbcon
 code, set fb_info.fbcon_rotate_hint when the panel is not mounted upright
 and we cannot use hardware rotation

Changes in v4:
-Make drm_fb_helper_init() init drm_fb_helper_crtc.rotation to
 DRM_MODE_ROTATE_0 for all crtcs, so that we do not end up setting the
 plane_state's rotation to an invalid value for disabled crtcs
 (caught by Fi.CI)

Changes in v5:
-Only use hardware (crtc primary plane) rotation for DRM_ROTATE_180,
 90 / 270 degree rotation requires special handling which we lack atm
-Add a TODO comment for 90 / 270 degree hardware rotation
-Add some comments to better document the default case when mapping
 sw_rotations to fbcon_rotate_hints

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=94894


Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171125193553.23986-5-hdegoede@redhat.com