override setpc macro so that sv can redirect it in branch

override setpc macro so that sv can redirect it in branch

this is slightly complicated.  setpc is a global macro, intended for
use in the templates.  however for SV it needs to be conditional,
so needs to redirect to a function in sv_insn_t.

that in turn needs quite a few extra parameters: the current loop
element offset, the argument to set_pc just in case actually it is
detected that this really is to be a branch not a predication scenario
and so on.

have not tried out vectorisation yet, at least straight non-vectorised
branch operations (unit tests) pass.