[mips] Fix inconsistent .cprestore behaviour between direct object emission and assembling.

Summary:
Direct object emission has an initialization order problem where an
InitMCObjectFile is called after MipsTargetELFStreamer determines whether
PIC is enabled by default or not. There doesn't seem to be point that
initializes all cases so split the responsibility between
MipsTargetELFStreamer and MipsAsmPrinter.

Reviewers: sdardis

Subscribers: dsanders, llvm-commits, sdardis

Differential Revision: http://reviews.llvm.org/D19728

llvm-svn: 268737