enable padlock on x86_64

[Sebastian Andrzej Siewior <sebastian@breakpoint.cc>]

To enable the padlock unit, two msr bits have to flipped. This is allready
done in the 32bit path and is missing in the other. Instead of copy paste
the code, I merged the 64bit part into the 32bit part. The things that
changed during the merge:
- the fixups from x86_64 (family 6, model >= 15) were not present in 32bit
  path but are now. They might be usefull if this CPU is booted in 32bit
  mode.
- the fixups which are executed via ->c_early_init() are now executed
  again via ->c_init(). This was done in the 64bit path and without this I
  lost the constant_tsc flag. However, tsc is not useable due to
| [    2.023006] Marking TSC unstable due to TSC halts in idle
| [    2.500082] Clocksource tsc unstable (delta = -326436711 ns)

The two patches are against the current tip tree. A version of patch 1
against current -rc8 is available at [0].

[0] http://download.breakpoint.cc/0001-x86-centaur-merge-32-64-bit-version.patch

Sebastian