microblaze: remove undefined of_get_cpu_node declaration

This patch removes the declaration of the function 'of_get_cpu_node'
which is not defined for microblaze. This is in preparation to move
it's definition from PPC to DT common code.

Michal Simek says: "it was just there because Microblaze
was based on powerpc code"
Acked-by: NMichal Simek <monstr@monstr.eu>
Signed-off-by: NSudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>

arch/microblaze/include/asm/prom.h

@@ -50,9 +50,6 @@ void of_parse_dma_window(struct device_node *dn, const void *dma_window_prop,
 
 extern void kdump_move_device_tree(void);
 
-/* CPU OF node matching */
-struct device_node *of_get_cpu_node(int cpu, unsigned int *thread);
-
 #endif /* __ASSEMBLY__ */
 #endif /* __KERNEL__ */