target/microblaze: Reorganize branching

target/microblaze: Reorganize branching

Remove the btaken variable, and simplify things by always computing
the full branch destination into btarget.  This avoids all need for
sync_jmpstate().

Retain the direct branch behaviour by remembering the jump destination
in jmp_dest, discarding btarget.  In the normal case, where the branch
delay slot cannot trap (e.g. arithmetic), tcg will remove the computation
into btarget, leaving us with just the tcg direct branching at the end.

Tested-by: Edgar E. Iglesias <[email protected]>
Reviewed-by: Edgar E. Iglesias <[email protected]>
Signed-off-by: Richard Henderson <[email protected]>