drm/i915/dsc: Check if vblank is sufficient for dsc prefill

drm/i915/dsc: Check if vblank is sufficient for dsc prefill

High refresh rate panels which may have small line times
and vblank sizes, Check if vblank size is sufficient for
dsc prefill latency.

--v2:
- Consider chroma downscaling factor in latency calculation. [Ankit]
- Replace with appropriate function name.

--v3:
- Remove FIXME tag.[Ankit]
- Replace Ycbcr444 to Ycbcr420.[Ankit]
- Correct precision. [Ankit]
- Use some local valiables like linetime_factor and latency to
adjust precision.
- Declare latency to 0 initially to avoid returning any garbage values.
- Account for second scaler downscaling factor as well. [Ankit]

--v4:
- Improvise hscale and vscale calculation. [Ankit]
- Use appropriate name for number of scaler users. [Ankit]
- Update commit message and rebase.
- Add linetime and cdclk prefill adjustment calculation. [Ankit]

--v5:
- Update bspec link in trailer. [Ankit]
- Correct hscale, vscale datatype. [Ankit]
- Use intel_crtc_compute_min_cdclk. [Ankit]

--v6:
- Use cdclk_state->logical.cdclk instead of
intel_crtc_compute_min_cdclk. [Ankit]

--v7:
- Fix linetime calculation. [Ankit]
- Reduce redandancy use of variables. [Ankit]
- Fix typos. [Ankit]
- Update calculation for precision. [Ankit]

--v8:
- Initialise variable to return garbage later. [Ankit]
- Initialise few variables to use at local loop, where
it is used. [Ankit]

Bspec: 70151
Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250120172209.188488-8-mitulkumar.ajitkumar.golani@intel.com