The linetime watermarks really have very little in common with the
plane watermarks. It looks to be cleaner to simply track them in
the crtc_state and program them from the normal modeset/fastset
paths.

The only dark cloud comes from the fact that the register is
still supposedly single buffered. So in theory it might still
need some form of two stage programming. Note that even though
HSW/BDWhave two stage programming we never computed any special
intermediate values for the linetime watermarks, and on SKL+
we don't even have the two stage stuff plugged in since everything
else is double buffered. So let's assume it's all fine and
continue doing what we've been doing.

Actually on HSW/BDW the value should not even change without
a full modeset since it doesn't account for pfit downscaling.
Thus only fastboot might be affected. But on SKL+ the pfit
scaling factor is take into consideration so the value may
change during any fastset.

As a bonus we'll plug this thing into the state
checker/dump now.

v2: Rebase due to bigjoiner prep
v2: Only compute ips linetime for IPS capable pipes.
    Bspec says the register values is ignored for other
    pipes, but in fact it can't even be written so the
    state checker becomes unhappy if we don't compute
    it as zero.

Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200120174728.21095-3-ville.syrjala@linux.intel.comReviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>