[mips] Remove ByValArgInfo::Address in favour of CCValAssign::getMemLocOffset(). NFC.

Summary: ByValArgInfo is practically the same as CCState::ByValInfo now.

Reviewers: vmedic

Reviewed By: vmedic

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D5976

llvm-svn: 221057