Aarch64 system registers known to binutils

[Jan Beulich]

Hello,

some time after seeing a051e2f3e0c1 ("[AArch64][gas] Update MTE system
register encodings") I went and checked my own disassembler as well as
gas against the doc, and I think there are a number of omissions in
binutils. The question is whether this is intentional, and registers
get added only as people find a need for having a (direct) way to
access them by name, or whether omissions here are to be considered
bugs.

Thanks for any insight,
Jan