Add Triple::isMIPS()/isMIPS32()/isMIPS64(). NFC

There are quite a few if statements that enumerate all these cases. It gets
even worse in our fork of LLVM where we also have a Triple::cheri (which
is mips64 + CHERI instructions) and we had to update all if statements that
check for Triple::mips64 to also handle Triple::cheri. This patch helps to
reduce our diff to upstream and should also make some checks more readable.

Reviewed By: atanasyan

Differential Revision: https://reviews.llvm.org/D48548

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335493 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCObjectFileInfo.cpp

@@ -529,8 +529,7 @@ void MCObjectFileInfo::initELFMCObjectFileInfo(const Triple &T, bool Large) {
   // MIPS .debug_* sections should have SHT_MIPS_DWARF section type
   // to distinguish among sections contain DWARF and ECOFF debug formats.
   // Sections with ECOFF debug format are obsoleted and marked by SHT_PROGBITS.
-  if (T.getArch() == Triple::mips || T.getArch() == Triple::mipsel ||
-      T.getArch() == Triple::mips64 || T.getArch() == Triple::mips64el)
+  if (T.isMIPS())
     DebugSecType = ELF::SHT_MIPS_DWARF;
 
   // Debug Info Sections.