[CodeGen][mips] Support `long_call/far/near` attributes

This patch adds support for the `long_call`, `far`, and `near` attributes
for MIPS targets. The `long_call` and `far` attributes are synonyms. All
these attributes override `-mlong-calls` / `-mno-long-calls` command
line options for particular function.

Differential revision: https://reviews.llvm.org/D35479

llvm-svn: 308667