powerpc/machdep: remove suspend_disable_cpu()

There are no users left of the suspend_disable_cpu() callback, remove
it.
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201207215200.1785968-21-nathanl@linux.ibm.com

arch/powerpc/include/asm/machdep.h

@@ -207,7 +207,6 @@ struct machdep_calls {
 	void (*suspend_disable_irqs)(void);
 	void (*suspend_enable_irqs)(void);
 #endif
-	int (*suspend_disable_cpu)(void);
 
 #ifdef CONFIG_ARCH_CPU_PROBE_RELEASE
 	ssize_t (*cpu_probe)(const char *, size_t);