drm/amd/pm: correct mem_busy_percent display due to calculation errors

drm/amd/pm: correct mem_busy_percent display due to calculation errors

PMFW may return invalid values due to internal calculation errors.
so, the kmd driver must validate and sanitize the returned values to
prevent issues caused by firmware calculation errors.

For example, values 0xfffe (-2) and 0xffff (-1) are treated
as invalid and clamped to 0.

this applies to devices with CAB (Cache As Buffer) functionality.

Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/4905
Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>