x86/tty/serial/8250: Clean up the asm/serial.h include file a bit

 - correct spelling
 - align fields vertically to make things more readable
 - make the layout of magic defines more obvious

Cc: Mark Rustad <mark.d.rustad@intel.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Link: http://lkml.kernel.org/r/1409972149-26272-1-git-send-email-jeffrey.t.kirsher@intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>