target-i386: Purely cosmetic integration.

This modifies files under target-i386 to get stylistic-only changes
from upstream (QEMU 2.0.0), i.e.:

- in cpu.h: Remove the EAX, EBX, ... DF macros and replace them with
  direct access to env->eip, env->df or env->regs[] instead.

- add or refine declarations in cpu.h, but doesn't modify behaviour.

- Add opening / closing braces where appropriate.

Change-Id: Ie4a024ff6ed6db9bb7d843221f4ad1fb59af925f