add mtvec_addr_i port
Created by: silabs-PaulZ
MTVEC will reset to mtvec_addr_i during first cycle of boot up.
Fixes issue https://github.com/openhwgroup/cv32e40p/issues/401
Requires RTL changes from: https://github.com/openhwgroup/cv32e40p/pull/403
Signed-off-by: Paul Zavalney paul.zavalney@silabs.com