Implement emit_jump when target is in register.

Bug: v8:6600
Change-Id: Idd8fc739ac9997cad53feffdfcee5ae25d9ad6ee
Reviewed-on: https://chromium-review.googlesource.com/1030453Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#52816}