drm/v3d: Expose memory stats through fdinfo

Use the common DRM function `drm_show_memory_stats()` to expose standard
fdinfo memory stats.

V3D exposes global GPU memory stats through debugfs. Those stats will be
preserved while the DRM subsystem doesn't have a standard solution to
expose global GPU stats.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240711142736.783816-1-mcanal@igalia.com