x86/amd_nb: Clean up init path

The initcall had unnecessary pr_notice() messages which are useless
noise on distro kernels.

Also, push the GART init error message where it belongs, *after* the
check whether the current hw we're loaded on, supports GART at all.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Battersby <tonyb@cybernetics.com>
Link: http://lkml.kernel.org/r/1466097230-5333-3-git-send-email-bp@alien8.de


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