4531b8ace4
Without this, somebody trying to map a buffer for write by the CPU would fail. This is not common to do in hardware driver environments, but it shouldn't be disallowed, and there's no downside to allowing it. I did skip virgl, because that's one where I don't know for sure if there wouldn't be a downside to allowing RDWR (there are other virt exports where RDWR is gated on a mappable flag). This is a follow-up to !37088 to keep copy and paste from introducing the same bug anywhere else. Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37339>