MIPS: asm: page: Allow __pa_symbol overrides

This will allow platforms to use an alternative way to get
the physical address of a symbol.
Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>

arch/mips/include/asm/page.h

@@ -190,7 +190,9 @@ typedef struct { unsigned long pgprot; } pgprot_t;
  * https://patchwork.linux-mips.org/patch/1541/
  */
 
+#ifndef __pa_symbol
 #define __pa_symbol(x)	__pa(RELOC_HIDE((unsigned long)(x), 0))
+#endif
 
 #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)