Introduce virt_to_phys()

virt_to_phys() returns the physical address given a virtual. In most
cases this will be just the input value as the vast majority of
systems run in a 1:1 mode.

However in systems that are not running this way it should report the
physical address or ~0 if no mapping exists for the given virtual
address.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

include/asm-microblaze/io.h

@@ -155,4 +155,9 @@ static inline void unmap_physmem(void *vaddr, unsigned long flags)
 
 }
 
+static inline phys_addr_t virt_to_phys(void * vaddr)
+{
+	return (phys_addr_t)(vaddr);
+}
+
 #endif /* __MICROBLAZE_IO_H__ */