ext: Add SoftFloat Library to ext directory

This patch adds Softfloat library for supporting RISCV
float operation implement.

Using SoftFloat Package to reinplement Riscv FPops.

Jira Issue: https://gem5.atlassian.net/browse/GEM5-373

Change-Id: Ic96e6c8adec0713bdbd744d581c750034b88246c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39357
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
228 files changed