Bug : MTVEC only support Direct mode

Created by: AyoubJalali

This is a bug for cv32a65x configuration !! According to the CV32A65X Spec, the mtvec only support direct mode, so the mtvec[1:0] should be always equal to zero, this is not the case for spike that support both direct and vectored mode.

the bug appears in both solo and tandem mode