drm/i915/display: Use ceiling division for NV12 UV surface offset calculation

drm/i915/display: Use ceiling division for NV12 UV surface offset calculation

For LNL+, odd source size and panning for YUV 422/420 surfaces is
supported. However, it requires the UV (chroma) surface Start X/Y and
width/height to be calculated as ceiling(half of Y plane value) rather
than floor.

The current code uses (>> 17) which combines the U16.16 fixed-point to
integer conversion (>> 16) with a divide-by-2 for chroma subsampling
(>> 1) into a single floor division. For odd Y plane values this
produces an off-by-one error in the UV plane offset.

On Android systems we see PLANE ATS fault when NV12 overlays are
used with odd source dimensions:

[  126.854200] xe 0000:00:02.0: [drm:intel_atomic_setup_scaler [xe]] [CRTC:148:pipe A] attached scaler id 0.0 to PLANE:33
[  126.854617] xe 0000:00:02.0: [drm:skl_update_scaler [xe]] [CRTC:148:pipe A] scaler_user index 0.0: staged scaling request for 1279x719->1340x753
[  126.854837] xe 0000:00:02.0: [drm:intel_plane_atomic_check [xe]] UV plane [PLANE:33:plane 1A] using Y plane [PLANE:123:plane 4A]
[  126.854926] xe 0000:00:02.0: [drm] *ERROR* [CRTC:148:pipe A] PLANE ATS fault

With Y plane width 1279:
  floor(1279/2) = 639 (current)
  ceil(1279/2)  = 640 (required)

Introduce fp_16_16_div2() and fp_16_16_to_int_ceil() helpers to cleanly
separate the two operations: first halve the U16.16 fixed-point value
for chroma subsampling (staying in fixed-point domain), then convert
to integer with ceiling rounding.

v2: Use DIV_ROUND_UP(value, 1 << 17) to preserve sub-pixel precision
    while making the ceiling division readable (Jani, Uma)

v3: Split into two helpers - fp_16_16_div2() for fixed-point division
    by 2 and fp_16_16_to_int_ceil() for ceiling conversion to integer,
    cleanly separating chroma subsampling from fixed-point to integer
    conversion (Jani)

Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patch.msgid.link/20260415165849.187693-1-vidya.srinivas@intel.com