gallium: Use fuchsia_open to avoid libfdio

Bug:434062283
Change-Id: I9c540fb4e0b78d824c0d3dda1fd2b605b76e1273
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/1330620
Fuchsia-Auto-Submit: Craig Stout <cstout@google.com>
Commit-Queue: Craig Stout <cstout@google.com>
Reviewed-by: David Gilhooley <dgilhooley@google.com>