x86/mm/pat: Initialize __cachemode2pte_tbl[] and __pte2cachemode_tbl[] in a bit more readable fashion

The initialization of these two arrays is a bit difficult to follow:
restructure it optically so that a 2D structure shows which bit in
the PTE is set and which not.

Also improve on comments a bit.

No code or data changed:

  # arch/x86/mm/init.o:

   text    data     bss     dec     hex filename
   4585     424   29776   34785    87e1 init.o.before
   4585     424   29776   34785    87e1 init.o.after

md5:
   a82e11ff58bcfd0af3a94662a701f65d  init.o.before.asm
   a82e11ff58bcfd0af3a94662a701f65d  init.o.after.asm
Reviewed-by: NJuergen Gross <jgross@suse.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20150305082135.GB5969@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>