[X86][Asm]Allow far jmp/call to be picked when using explicit FWORD size specifier

Currently, far jmp/call which utilizes a 48bit memory operand would have been invoked via the 'lcall/ljmp' mnemonic (intel style).
This patch align those variants to formal intel spec

Differential Revision: https://reviews.llvm.org/D35846

llvm-svn: 310485