make.sh: execute "make mrproper" when first compile

fix compile issue while git checkout between rkdevelop and next-dev:

  Using /home/cjh/uboot-nextdev/u-boot as source for U-Boot
  /home/cjh/uboot-nextdev/u-boot is not clean, please run 'make mrproper'
  in the '/home/cjh/uboot-nextdev/u-boot' directory.
make[1]: *** [prepare3] Error 1
make[1]: *** Waiting for unfinished jobs....

Change-Id: If9e01b407f524360ff402d8d36241f3885c90c48
Signed-off-by: Joseph Chen <chenjh@rock-chips.com>

make.sh

@@ -51,6 +51,13 @@ prepare()
 		echo "	3. Download full release SDK Responsity"
 		exit 1
 	fi
+
+	# Clean! We assume that ./u-boot.map indicates U-Boot project is not clean,
+	# maybe git checkout from rkdevelop.
+	if [ -f ./u-boot.map ]; then
+		make mrproper
+		echo "auto \"make mrproper\" done..."
+	fi
 }
 
 select_toolchain()
@@ -146,9 +153,9 @@ pack_trust_image()
 }
 
 prepare
-select_toolchain
 echo "make for ${BOARD}_defconfig by -j${JOB}"
 make ${BOARD}_defconfig O=${DSTDIR}/out
+select_toolchain
 make CROSS_COMPILE=${TOOLCHAIN_GCC}  all --jobs=${JOB} O=${DSTDIR}/out
 fixup_chip_name
 pack_loader_image