[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/arch/mips/Makefile b/arch/mips/Makefile
index 4337c49..ce7e02e 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -577,19 +577,17 @@
 # Automatically detect the build format. By default we choose
 # the elf format according to the load address.
 # We can always force a build with a 64-bits symbol format by
-# passing 'BUILD_ELF32=no' option to the make's command line.
+# passing 'KBUILD_SYM32=no' option to the make's command line.
 #
 ifdef CONFIG_64BIT
-  ifndef BUILD_ELF32
+  ifndef KBUILD_SYM32
     ifeq ($(shell expr $(load-y) \< 0xffffffff80000000), 0)
-      BUILD_ELF32 = y
+      KBUILD_SYM32 = y
     endif
   endif
 
-  ifeq ($(BUILD_ELF32), y)
-    cflags-y += -msym32
-  else
-    cflags-y += -DCONFIG_BUILD_ELF64
+  ifeq ($(KBUILD_SYM32), y)
+    cflags-y += -msym32 -DKBUILD_64BIT_SYM32
   endif
 endif