drm/vmwgfx: Fix implicit declaration error

The declarations of ttm_range_man_init and ttm_range_man_fini
have been moved to ttm_range_manager.h so we have to add it
to the include list.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Fixes: 3eb7d96e

 ("drm/ttm: flip over the range manager to self allocated nodes")
Cc: Christian König <christian.koenig@amd.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210609172307.131929-10-zackr@vmware.com