x86/mce/amd: Cleanup threshold device remove path

Pass in the bank pointer directly to the cleaning up functions,
obviating the need for per-CPU accesses. Make the clean up path
interrupt-safe by cleaning the bank pointer first so that the rest of
the teardown happens safe from the thresholding interrupt.

No functional changes.

 [ bp: Write commit message and reverse bank->shared test to save an
   indentation level in threshold_remove_bank(). ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200403161943.1458-7-bp@alien8.de

arch/x86/include/asm/amd_nb.h

@@ -57,6 +57,7 @@ struct threshold_bank {
 
 	/* initialized to the number of CPUs on the node sharing this bank */
 	refcount_t		cpus;
+	unsigned int		shared;
 };
 
 struct amd_northbridge {