'Illegal Instruction' when executing sign and zero extend functions when destination LMUL=8

[ParkerJones567]

Hello Vicuna community,

I have run into issues executing vsext.vf2 and vzext.vf2 functions with a destination LMUL=8. When attempting to execute these, an 'Illegal Instruction' exception is thrown. I believe that they should all be supported by the Zve32x extension.

To reproduce this issue, I have added a few tests under vicuna/test/alu named:

vsext_vf2_i16m8 - Sign extend from i8m4 to i16m8
vsext_vf2_i32m8 - Sign extend from i16m4 to i32m8
vzext_vf2_i16m8 - Zero extend from i8m4 to i16m8
vzext_vf2_i32m8 - Zero extend from i16m4 to i32m8

These can be found at the fork here: https://github.com/PhilippvK/vicuna

This issue may be related to #75

Thanks!

J Parker Jones