drm/xe: Make read_perf_limit_reasons globally accessible

Other driver code beyond the sysfs interface wants to know about
throttling. So make the query function globally accessible.

v2: Revert include order change (review feedback from Lucas)
v3: Remove '_sysfs' from throttle file names and keep limit query in
the same file rather than moving elsewhere (review feedback from
Rodrigo).
v4: Correct #include while renaming header file (review feedback
from Lucas).

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240518043700.3264362-2-John.C.Harrison@Intel.com