[MIPS] Rename CONFIG_BUILD_ELF64 into KBUILD_64BIT_SYM32

This patch renames it for 3 reasons:

    - "CONFIG" pattern is used by Kconfig. Now this macro is
      no more defined by Kconfig but by Kbuild itself make this
      clear by translating "CONFIG" into "KBUILD".

    - "ELF32" word is improper because it is irrelevant to ELF
      format and it makes confusion with CONFIG_BOOT_ELF32. So
      translate it with SYM32.

    - Add "64BIT" part to make clear that this macro implies a
      64 bits kernel.

Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/include/asm-mips/pgtable-64.h b/include/asm-mips/pgtable-64.h
index 49f5a1a..a8aed9c 100644
--- a/include/asm-mips/pgtable-64.h
+++ b/include/asm-mips/pgtable-64.h
@@ -104,7 +104,7 @@
 #define VMALLOC_START		MAP_BASE
 #define VMALLOC_END	\
 	(VMALLOC_START + PTRS_PER_PGD * PTRS_PER_PMD * PTRS_PER_PTE * PAGE_SIZE)
-#if defined(CONFIG_MODULES) && !defined(CONFIG_BUILD_ELF64) && \
+#if defined(CONFIG_MODULES) && defined(KBUILD_64BIT_SYM32) && \
 	VMALLOC_START != CKSSEG
 /* Load modules into 32bit-compatible segment. */
 #define MODULE_START	CKSSEG