Revert "[ARM] unconditionally define __virt_to_phys and __phys_to_virt"

This reverts commit 75f4aa15.

We have a couple of platforms which require non-linear P:V mappings,
so we need these to be overridable.
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/memory.h

@@ -125,8 +125,10 @@
  * private definitions which should NOT be used outside memory.h
  * files.  Use virt_to_phys/phys_to_virt/__pa/__va instead.
  */
+#ifndef __virt_to_phys
 #define __virt_to_phys(x)	((x) - PAGE_OFFSET + PHYS_OFFSET)
 #define __phys_to_virt(x)	((x) - PHYS_OFFSET + PAGE_OFFSET)
+#endif
 
 /*
  * Convert a physical address to a Page Frame Number and back