KVM: x86 emulator: X86EMUL macro replacements: x86_emulate_insn() and its helpers

This patch just replaces integer values used inside
x86_emulate_insn() and its helper functions to X86EMUL_*.

The purpose of this is to make it clear what will happen
when the variable rc is compared to X86EMUL_* at the end
of x86_emulate_insn().

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>