AArch64/ARM64: accept and print floating-point immediate 0 as "#0.0"

It's been decided that in the future, the floating-point immediate in
instructions like "fcmeq v0.2s, v1.2s, #0.0" will be canonically "0.0", which
has been implemented on AArch64 already but not ARM64.

This fixes that issue.
AArch64/ARM64: add specific diagnostic for MRS/MSR and enable tests.
AArch64/ARM64: implement remaining TLS relocations (purely MC).
ARM64: print fp immediates without using scientific notation.