MIPS: Fix DIRECT_API_CALL_NEW and DIRECT_GETTER_CALL_NEW call.

MIPS: Fix DIRECT_API_CALL_NEW and DIRECT_GETTER_CALL_NEW call.

This commit fixes the register usage of DIRECT_API_CALL_NEW
and DIRECT_GETTER_CALL_NEW:

* These functions expect arguments in a0-a1 and not in a1-a2
  as the and DIRECT_API_CALL and DIRECT_GETTER_CALL do.
* Fixes the simulator to expect *_NEW arguments in a0-a1.
* Adds more comment to simulator to better explain the
  register usage.

TEST=cctest/test-api/LoadICFastApi_DirectCall_GCMoveStub,cctest/test-api/SimpleCallback

BUG=

Committed: https://code.google.com/p/v8/source/detail?r=14813

[Paul Lind, 2013-05-25 15:51:31]

lgtm, thanks!

[palfia, 2013-05-25 17:10:50]

Committed manually as r14813 (presubmit successful).