[mips] Wrong register usage in LLInt.

Fix register usage and add PIC header to all LLInt operations.
This patch is taken from https://bugs.webkit.org/show_bug.cgi?id=125168.

It fixes the crash of fast/js/exception-propagate-from-dfg-to-llint test
on mips architecture.

Change-Id: I98ad3b5766451cab48a76f7e028b210f9ebe99ed
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@digia.com>