build:arm allow to store build settings in a .settings file.

if present source a file called .settings when calling the
arm_sdimage.sh script.  This allows to configure the build
setting of arm build without the need to specify the flags
each time arm_sdimage.sh is called.

for example to configure the arm_sdimage.sh to target the
beaglebone put the following content in your .settings file.

BASE_URL=http://www.minix3.org/arm/beaglebone
FLAG=-DAM335X
CONSOLE=tty00

Change-Id: Ide0341a255bc7f41dc5c30d0a43e71b01a8ea55c

releasetools/arm_sdimage.sh

@@ -2,6 +2,15 @@
 set -e
 #set -x
 
+#
+# Source settings if present
+#
+if [ -e .settings ]
+then
+	echo "Sourcing settings frem .settings"
+ 	. .settings
+fi
+
 : ${ARCH=evbearm-el}
 : ${OBJ=../obj.${ARCH}}
 : ${CROSS_TOOLS=${OBJ}/"tooldir.`uname -s`-`uname -r`-`uname -m`"/bin}