drm/i915: Add explicit pipe src size to pipe config

Rather that mess about with hdisplay/vdisplay from requested_mode, add
explicit pipe src size information to pipe config.

Now requested_mode is only really relevant for dvo/sdvo output timings.
For everything else either adjusted_mode or pipe src size should be
used.

In many places where we end up using pipe source size, we should
actually use the primary plane size, but we don't currently store
that information explicitly. As long as we treat primaries as full
screen only, we can get away with this. Eventually when we move
primaries over to drm_plane, we need to fix it all up.

v2: Add a comment to explain what pipe_src_{w,h} are
    Add a note about primary planes to commit message

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>