drm/v3d: Show the memory-management stats on debugfs

Dump the contents of the DRM MM allocator of the V3D driver. This will
help us to debug the VA ranges allocated.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240105145851.193492-1-mcanal@igalia.com