This is the implementation of crrev.com/c/766371 for mips.

Original description:

Add the ability to return (multiple) return values on the stack:

- Extend stack frames with a new buffer region for return slots.
  This region is located at the end of a caller's frame such that
  its slots can be indexed as caller frame slots in a callee
  (located beyond its parameters) and assigned return values.
- Adjust stack frame constructon and deconstruction accordingly.
- Extend linkage computation to support register plus stack returns.
- Reserve return slots in caller frame when respective calls occur.
- Introduce and generate architecture instructions ('peek') for
  reading back results from return slots in the caller.
- Aggressive tests.
- Some minor clean-up.

R=v8-mips-ports@googlegroups.com

Change-Id: I2f30cc297771ec74b0b935b6ea28d3d61a986d5c
Reviewed-on: https://chromium-review.googlesource.com/839660Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50272}