[PPC64] Add support for clrbhrb, mfbhrbe, rfebb.

This patch adds support for the ISA 2.07 additions involving the
branch history rolling buffer and event-based branching.  These will
not be used by typical applications, so built-in support is not
required.  They will only be available via inline assembly.

Assembly/disassembly tests are included in the patch.

llvm-svn: 238032
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 81589c8..c93de43 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -275,6 +275,16 @@
       /// operand identifies the operating system entry point.
       SC,
 
+      /// CHAIN = CLRBHRB CHAIN - Clear branch history rolling buffer.
+      CLRBHRB,
+
+      /// GPRC, CHAIN = MFBHRBE CHAIN, Entry, Dummy - Move from branch
+      /// history rolling buffer entry.
+      MFBHRBE,
+
+      /// CHAIN = RFEBB CHAIN, State - Return from event-based branch.
+      RFEBB,
+
       /// VSRC, CHAIN = XXSWAPD CHAIN, VSRC - Occurs only for little
       /// endian.  Maps to an xxswapd instruction that corrects an lxvd2x
       /// or stxvd2x instruction.  The chain is necessary because the