svga/drm: use pb_usage_flags instead of pipe_map_flags in vmw_svga_winsys_buffer_map

This patch basically maps pipe_map_flags to pb_flags. Since we are mapping it, STATIC_ASSERTS won't be required.

Fixes: 00c30dad ("gallium: renumber PIPE_MAP_* enums to remove holes")

Reviewed-by: Charmaine Lee charmainel@vmware.com