MIPS64: Fix hidden bug in relocations for j and jal.

MIPS64: Fix hidden bug in relocations for j and jal.

Introduce new mechanism for relocating j/jal.

Resolves flaky failures of mozilla regress tests.

Additionally:

- internal encoded references are not relocated during code generation phase.
- remove asserts from j and jal which are not
valid because addresses are not final and valid in code generation phase.

TEST=mozilla/js1_5/Regress/regress-280769-2, regress-367561-01,
     mozilla/ecma_3/Statements/regress-444979
BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/1216823003 .

Patch from dusan.milosavljevic <dusan.milosavljevic@imgtec.com>.

Cr-Commit-Position: refs/heads/master@{#29962}