panfrost: Add NATIVE_FENCE_FD capability
Add support for NATIVE_FENCE_FD so our can advertise support for EGL_ANDROID_native_fence_sync.
Our submit path currently waits for both the explicit fence (ctx::in_sync_fd) and our internal fence (which is used to serialize access to the tiler context), when some drivers, like VC4, just replace the internal fence wait by the explicit one when present. Not sure if there's some guarantees that makes this additional wait-on-internal-sync useless, but I thought I'd stay on the safe side and wait for comments before changing that.
/cc @cphealy for testing /cc @anholt or @chadversary or @robclark for reviews