Add makeem convenience script

This script will build U-Boot for all Boundary Devices
boards and memory configurations.

Usage is:
	~/u-boot-imx6$ export CROSS_COMPILE=arm-linux-gnueabihf-
	~/u-boot-imx6$ . makeem

Binaries for each will be saved in the save/ directory
and named u-boot.configname.

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>