drm/xe/gt_stats: Use atomic64_t for counters

drm/xe/gt_stats: Use atomic64_t for counters

The stats counters are now used for things like counting the VMA
bytes during page faults. During workload execution, the counter
value can grow fast and easily reach the atomic int limit, in
which case it overflows. To make this less likely to happen, push
the limit by switching to 64b atomic to store the counter value.
Overhead is very small as there are only 3 stat entries per GT as
of now, and stats are only enabled with CONFIG_DEBUG_FS.

Suggested-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250225195902.1247100-2-francois.dugast@intel.com
Signed-off-by: Francois Dugast <francois.dugast@intel.com>