drm/amd/display: Fix Signed/Unsigned Int Usage Compiler Warning

drm/amd/display: Fix Signed/Unsigned Int Usage Compiler Warning

[Why] Compiler generates compiler warnings when signed enum
constants or literal -1 are implicitly converted to unsigned
integer types, cluttering build output and masking genuine issues.

[How] Use UINT_MAX as the invalid sentinel for unsigned IDs and align
loop/index types to unsigned where appropriate to remove implicit
signed-to-unsigned conversions, with no functional behavior change.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Gaghik Khachatrian <gaghik.khachatrian@amd.com>
Signed-off-by: Chuanyu Tseng <chuanyu.tseng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>