AVR32: Use avr32-linux- cross-compilation prefix by default

It doesn't really matter which toolchain you use to compile u-boot,
but the avr32-linux one is probably what most people have installed.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

Makefile

@@ -149,7 +149,7 @@ ifeq ($(ARCH),blackfin)
 CROSS_COMPILE = bfin-uclinux-
 endif
 ifeq ($(ARCH),avr32)
-CROSS_COMPILE = avr32-
+CROSS_COMPILE = avr32-linux-
 endif
 endif
 endif