drm/i915: Store plane relative data rate in crtc_state

drm/i915: Store plane relative data rate in crtc_state

Store the relative data rate for planes in the crtc state
so that we don't have to use
intel_atomic_crtc_state_for_each_plane_state() to compute
it even for the planes that are no part of the current state.

Should probably just nuke this stuff entirely an use the normal
plane data rate instead. The two are slightly different since this
relative data rate doesn't factor in the actual pixel clock, so
it's a bit odd thing to even call a "data rate". And since the
watermarks are computed based on the actual data rate anyway
I don't really see what the point of this relative data rate
is. But that's for the future...

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201106173042.7534-6-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>