[llvm][AArch64] Fix "+all" feature for sysreg aliases

For example the predres extension adds one instruction that
is a sys alias. Previously this wasn't disassembled properly
with "+all".

This was because a check for "+all" was added to haveFeatures
in AArch64SysReg but not in SysAlias.

Reviewed By: MaskRay, lenary

Differential Revision: https://reviews.llvm.org/D129147