[AArch64] Add Fujitsu A64FX scheduling model

Basic support of A64FX was added in D75594 but its scheduling model
was missing. This commit adds the scheduling model. Also, this commit
amends/adds some subtarget parameters of A64FX.

The A64FX Microarchitecture Manual, which is source information of
this commit, is on GitHub.

https://github.com/fujitsu/A64FX/

Differential Revision: https://reviews.llvm.org/D93791