[mips] Emit R_MICROMIPS_GPREL16/R_MICROMIPS_SUB/R_MICROMIPS_LO16 / HI16 relocations

Emit R_MICROMIPS_GPREL16/R_MICROMIPS_SUB/R_MICROMIPS_LO16 and
R_MICROMIPS_GPREL16/R_MICROMIPS_SUB/R_MICROMIPS_HI16 chains of
relocations for %lo(%neg(%gp_rel())) and %hi(%neg(%gp_rel()))
expressions in case of microMIPS.

Differential Revision: http://reviews.llvm.org/D47220

llvm-svn: 333409