Add support for vnsrl and narrowing ops.

* vnsrl is a narrowing op, which required template changes to support
varying type widths.
* Add/modify vec_test_helpers module to support narrowing ops.
* Add softrvv vnsrl implementation and test.
* Add a compile time check to softrvv_vnsrl for SEW of dest is 1/2 SEW src2.
* Add vnsrl test.
* Modify softrvv templates for changes in vec_test_helpers module.

Change-Id: I5889200ea36e213dee9a051ae726ed3bf0480d3e
20 files changed