target-*: Unconditionally emit tcg_gen_insn_start

target-*: Unconditionally emit tcg_gen_insn_start

While we're at it, emit the opcode adjacent to where we currently
record data for search_pc.  This puts gen_io_start et al on the
"correct" side of the marker.

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>