[MIPS] Remove '-mno-explicit-relocs' option when CONFIG_BUILD_ELF64

This patch removes '-mno-explicit-relocs' usage when
CONFIG_BUILD_ELF64 is set since this option was only required
with the old hack to truncate addresses at the assembly level
where "-mabi=64 -Wa,-mabi=32" was used.

This should yield a small code size improvement for inline
assembly, where the R constraint is used.

The idea is coming from Maciej <macro@linux-mips.org>.
Signed-off-by: NFranck Bui-Huu <fbuihuu@gmail.com>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/Makefile

@@ -60,9 +60,7 @@ vmlinux-32		= vmlinux.32
 vmlinux-64		= vmlinux
 
 cflags-y		+= -mabi=64
-ifdef CONFIG_BUILD_ELF64
-cflags-y		+= $(call cc-option,-mno-explicit-relocs)
-else
+ifndef CONFIG_BUILD_ELF64
 cflags-y		+= $(call cc-option,-msym32)
 endif
 endif