tcg/i386: Check the size of instruction being translated

This fixes the bug: 'user-to-root privesc inside VM via bad translation
caching' reported by Jann Horn here:
https://bugs.chromium.org/p/project-zero/issues/detail?id=1122

Reviewed-by: Richard Henderson <rth@twiddle.net>
CC: Peter Maydell <peter.maydell@linaro.org>
CC: Paolo Bonzini <pbonzini@redhat.com>
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Message-Id: <20170323175851.14342-1-bobby.prani@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
static inline void gen_op_add_reg_T0(TCGMemOp size, int reg)
{
    tcg_gen_add_tl(cpu_tmp0, cpu_regs[reg], cpu_T0);
    gen_op_mov_reg_v(size, reg, cpu_tmp0);
}

static inline void gen_op_add_reg_T0(TCGMemOp size, int reg)
{
    tcg_gen_add_tl(cpu_tmp0, cpu_regs[reg], cpu_T0);
    gen_op_mov_reg_v(size, reg, cpu_tmp0);
}
