drm/i915: Reject modes with linetime > 64 usec

drm/i915: Reject modes with linetime > 64 usec

Reject modes whose linetime exceeds 64 usec.

First reason being that WM_LINETIME is limited to (nearly) 64 usec.

Additionally knowing the linetime is bounded will help with
determining whether overflows may be a concern during various
calculations.

I decided to round up, and accept the linetime==64 case. We use
various rounding directions for this in other parts of the code,
so I feel this provides the most consistent result all around.

Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20251014191808.12326-3-ville.syrjala@linux.intel.com