freedreno: Use explicit *_NONE enum for undefined formats

freedreno: Use explicit *_NONE enum for undefined formats

This adds RB, VFMT and TFMT NONE values for a3xx-a5xx and FMT6_NONE
for a6xx.  Use those values instead of open coded (enum xxx) ~0 or
sometimes even ~0, which triggers out-of-enum range warnings.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5173>