Change LEA to have 5 operands for its memory operand, just

Change LEA to have 5 operands for its memory operand, just
like all other instructions, even though a segment is not
allowed.  This resolves a bunch of gross hacks in the
encoder and makes LEA more consistent with the rest of the
instruction set.

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107934 91177308-0d34-0410-b5e6-96231b3b80d8