socfpga_mkimage: Fix/clarify error message ...

The actual max_image_size may be smaller than the define MAX_IMAGE_SIZE
due to the additional header needed, so print max_image_size in the
error message. Also, when complaining about a too big image say how big
the image actually is.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

scripts: Add Altera SoCFPGA mkimage support ...

The Altera SoCFPGAs expect a simple header for their first stage
loaders. This adds a tool to generate images for the SoCFPGAs. The
header is either embedded into the image or optionally prepended
to the image. In this case code is added to jump over the image
header.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>