arch-riscv: Add Zfh extension

This commit adds RISC-V Zfh 1.0 (half-precision IEEE 754 binary16 floating
point) extension to gem5. Include the following commands:

* FLH / FSH
* FMADD.H / FMSUB.H / FNMSUB.H / FNMADD.H
* FADD.H / FSUB.H / FMUL.H / FDIV.H
* FSQRT.H
* FSGNJ.H / FSGNJN.H / FSGNJX.H
* FMIN.H / FMAX.H
* FCVT.S.H / FCVT.H.S
* FCVT.D.H / FCVT.H.D
* FCVT.W.H / FCVT.H.W
* FCVT.WU.H / FCVT.H.WU
* FMV.X.H / FMV.H.X
* FEQ.H / FLT.H / FLE.H
* FCLASS.H
* FCVT.L.H / FCVT.H.L
* FCVT.LU.H / FCVT.H.LU

Change-Id: Id7870fdfa1aa8b840706c3ba2cab8eeaf008880f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/60029
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
6 files changed