arch-riscv: Using Softfloat Library to implements float operation

The Riscv float instruction could not pass riscv-tests. This patch
use Softfloat Library interface to implements float operation. The
riscv-tests float instruction tests now pass.

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

Change-Id: I2c95af8161a8d3f92c933aa82d797db5adebc574
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39735
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
5 files changed