[MIPS] Fix CONFIG_BUILD_ELF64 kernels with symbols in CKSEG0.

The __pa() for those did assume that all symbols have XKPHYS values and
the math fails for any other address range.

Signed-off-by: Ralf Baechle <[e-mail]>

include/asm-mips/page.h

···
 /*
  * __pa()/__va() should be used only during mem init.
  */
-#if defined(CONFIG_64BIT) && !defined(CONFIG_BUILD_ELF64)
+#ifdef CONFIG_64BIT
 #define __pa(x)								\
 ({									\
     unsigned long __x = (unsigned long)(x);				\