Build for PLATFORM=vexpress-qemu_virt by default

Also, for STM platforms, set CROSS_COMPILE=arm-linux-gnueabihf-
by default (which is a more standard prefix for the 32-bit
compiler).

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Pascal Brand <pascal.brand@linaro.org>
diff --git a/Makefile b/Makefile
index ad81a9c..29fed60 100644
--- a/Makefile
+++ b/Makefile
@@ -22,7 +22,8 @@
 
 # Make these default for now
 ARCH            ?= arm
-PLATFORM        ?= stm
+PLATFORM        ?= vexpress
+PLATFORM_FLAVOR ?= qemu_virt
 O		?= out/$(ARCH)-plat-$(PLATFORM)
 
 arch_$(ARCH)	:= y