[MC] Require an MCContext when constructing an MCDisassembler.

This patch re-introduces the MCContext member that was removed from
MCDisassembler in r206063, and requires that an MCContext be passed in at
MCDisassembler construction time. (Previously the MCContext member had been
initialized in an ad-hoc fashion after construction). The MCCContext member
can be used by MCDisassembler sub-classes to construct constant or
target-specific MCExprs.

This patch updates disassemblers for in-tree targets, and provides the
MCRegisterInfo instance that some disassemblers were using through the
MCContext (previously those backends were constructing their own
MCRegisterInfo instances).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206241 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM64/Disassembler/ARM64Disassembler.cpp

@@ -184,8 +184,9 @@ using namespace llvm;
 #define Fail llvm::MCDisassembler::Fail
 
 static MCDisassembler *createARM64Disassembler(const Target &T,
-                                               const MCSubtargetInfo &STI) {
-  return new ARM64Disassembler(STI);
+                                               const MCSubtargetInfo &STI,
+                                               MCContext &Ctx) {
+  return new ARM64Disassembler(STI, Ctx);
 }
 
 DecodeStatus ARM64Disassembler::getInstruction(MCInst &MI, uint64_t &Size,