[PATCH 0/8] aarch64 vector cost tweaks

[Richard Sandiford via Gcc-patches]

This patch series:

(1) generalises the aarch64 vector costs to allow for the final patch.
    This part should be a no-op for existing tuning code.

(2) tweaks the AARCH64_EXTRA_TUNE_USE_NEW_VECTOR_COSTS code.  This currently
    only affects neoverse-v1 and again helps with the final patch.

(3) adds a new -mtune=neoverse-512tvb option.  See the covering message
    in the final patch for details.

Tested on aarch64-linux-gnu and applied to trunk so far.  I'll backport
to GCC 11 in a few days if there is no fallout.  The patches should be
very low risk; as mentioned, (1) should be a no-op for existing targets
and (2) simply provides minor tweaks/fixes to -mtune code that was new
to GCC 11.

Thanks,
Richard