MIPS: Multiple stubs can point to the same calling convention.

Port r23546 (068adb0)

BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/525403003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23573 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: InterfaceDescriptor becomes CallInterfaceDescriptor.

Port r23560 (9a63ff6)

Original commit message:
There was no difference between these two classes in a hierarchical
relationship.

BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/530783003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23574 ce2b1a6d-e550-0410-aec6-3dcde31c8c00