drm/ttm: Balance ttm_resource_cursor_init() and ttm_resource_cursor_fini()

Make the interface more symmetric by providing and using a
ttm_resource_cursor_init().

v10:
- Fix a stray newline (Matthew Brost)
- Update kerneldoc (Matthew Brost)

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241217145852.37342-2-thomas.hellstrom@linux.intel.com


Signed-off-by: Christian König <christian.koenig@amd.com>