drm/i915/scaler: Add and compute scaling factors

Add scaling factors to scaler_state for a particular scaler user.
These factors will be used later to compute scaler prefill latency.
Currently, only plane scaling factors are stored, but the same members
can later be extended to store pipe scaling factors as well.

--v2:
- Rephrase commit message. [Ankit]
- Corrects typos. [Ankit]

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/20250120172209.188488-2-mitulkumar.ajitkumar.golani@intel.com