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