gallium/winsys: rename DRM_API_HANDLE_* to WINSYS_HANDLE_*

gallium/winsys: rename DRM_API_HANDLE_* to WINSYS_HANDLE_*

This just renames this as we want to add an shm handle which
isn't really drm related.

Originally by: Marc-André Lureau <marcandre.lureau@gmail.com>
(airlied: I used this sed script instead)
This was generated with:
 git grep -l 'DRM_API_' | xargs sed -i 's/DRM_API_/WINSYS_/g'

Reviewed-by: Marek Olšák <marek.olsak@amd.com>