drm/amd/display: Fix implicit narrowing conversions in modules

drm/amd/display: Fix implicit narrowing conversions in modules

[Why]: Implicit narrowing of wider integer types (unsigned int, uint64_t)
into narrower fields (uint8_t, uint16_t, unsigned short) has potential
truncation issues.

[How]: For each warning site, added ASSERT(<value> <= 0xFFFF/0xFF) for
debug-mode bounds verification followed by an explicit cast. Typed
intermediate variables introduced where needed for clarity.

No functional change intended.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Gaghik Khachatrian <gaghik.khachatrian@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>