drm/v3d: Do not use intermediate storage when copying performance query results

Removing the intermediate buffer removes the last use of the
V3D_MAX_COUNTERS define, which will enable further driver cleanup.

While at it pull the 32 vs 64 bit copying decision outside the loop in
order to reduce the number of conditional instructions.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240711135340.84617-9-tursulin@igalia.com