arch/mips: Set BR2_GCC_TARGET_ARCH for MIPS

Set --with-arch instead of --with-tune for MIPS so that the
generated code will be optimal for the given MIPS ISA.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

arch/Config.in.mips

@@ -72,7 +72,7 @@ config BR2_ENDIAN
 	default "LITTLE"	if BR2_mipsel || BR2_mips64el
 	default "BIG" 	    	if BR2_mips || BR2_mips64
 
-config BR2_GCC_TARGET_TUNE
+config BR2_GCC_TARGET_ARCH
 	default "mips1"		if BR2_mips_1
 	default "mips2"		if BR2_mips_2
 	default "mips3"		if BR2_mips_3