drm/i915: Remove all *_pipes flags from modeset

Set the mode_changed field on the crtc_states and use that instead.

Note that even though this patch doesn't completely replace the logic in
intel_modeset_affected_pipes(), that logic was never fully used to its
full extent. Since the commit mentioned below, modeset_pipes and
prepare_pipes would only contain at most the pipe for which the set_crtc
ioctl was called. We can grow back that logic when the time comes.

commit b6c5164d
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Apr 12 18:48:43 2013 +0200

    drm/i915: Fixup Oops in the pipe config computation

v2: Don't set mode_changed unconditionally for modeset_crtc. (Ander)
    Check for needs_modeset() before trying to allocate a PLL. (Ander)
    Only call .crtc_enable() for pipes that were disabled. (Maarten)
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>