[mips] Remove MipsCC::reservedArgArea() in favour of MipsABIInfo::GetCalleeAllocdArgSizeInBytes(). NFC.

Summary:

Reviewers: theraven, vmedic

Reviewed By: vmedic

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D6115


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221528 91177308-0d34-0410-b5e6-96231b3b80d8