[PATCH 0/3, 2.44?] aarch64: Assorted dependency fixes

[Andrew Carlotti]

All of these patches remove dependencies between features, which makes gas more
permissive for feature additions and more restrictive for feature removals.

Patches 1 and 2 address feature flags that were added in Binutils 2.42 and 2.43
respectively, and have not yet been released in GCC (I intend to amend the
dependencies there before the release of GCC 15).  I see no good reason to
specify the explicit removal of these features in a target string, so these
patches make gas more restrictive in all realistic scenarios.

Patch 3 makes gas strictly more permissive, and in particular enables support
for the target string  `-march=armv9-a+sme+nosve`.

Are these patches ok for master?  Additionally, if Nick and (a) Richard
approve, how about the 2.44 branch?