[ELF][MIPS] Exclude mips .got from PT_GNU_RELRO segment

On MIPS .got section cannot be included into the PT_GNU_RELRO segment.
Sometimes it might work, but in general it is unsupported. One of the
problem is that all sections marked by SHF_MIPS_GPREL should be grouped
together because data in these sections is addressable with a gp
relative address, but such sections might be writable.

This patch exclude mips .got from PT_GNU_RELRO segment and group
SHF_MIPS_GPREL sections.

llvm-svn: 292161