x86/mm/pat: Don't report PAT on CPUs that don't support it

The pat_enabled() logic is broken on CPUs which do not support PAT and
where the initialization code fails to call pat_init(). Due to that the
enabled flag stays true and pat_enabled() returns true wrongfully.

As a consequence the mappings, e.g. for Xorg, are set up with the wrong
caching mode and the required MTRR setups are omitted.

To cure this the following changes are required:

  1) Make pat_enabled() return true only if PAT initialization was
     invoked and successful.

  2) Invoke init_cache_modes() unconditionally in setup_arch() and
     remove the extra callsites in pat_disable() and the pat disabled
     code path in pat_init().

Also rename __pat_enabled to pat_disabled to reflect the real purpose of
this variable.

Fixes: 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled")
Signed-off-by: Mikulas Patocka <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Bernhard Held <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: "Luis R. Rodriguez" <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1707041749300.3456@file01.intranet.prod.int.rdu2.redhat.com

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