drm/amd/display: Fix compiler warnings

drm/amd/display: Fix compiler warnings

[Why] Implicit conversions from wider integer types to byte-sized fields
were generating compiler warnings. These warnings hide intentional protocol
/storage boundaries and reduce signal quality during builds. Making
conversion intent explicit improves readability and warning hygiene
without changing behavior.

[How] Added explicit, type-safe  casts at intentional narrow-storage
boundaries. Kept data models & runtime logic unchanged, only clarifying
conversion intent.

Functionality and behavior is unchanged; only type intent is explicit.
Aligned warning cleanup with existing coding standards for explicit
boundary conversions.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Gaghik Khachatrian <gaghik.khachatrian@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>