ARM omap spi image: print error to stderr ...

Since the utility outputs the image on stdout we have to print the
error messages to stderr in order to see them.

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

ARM omap spi image: relax size constrains ...

The omap spi utility requires the image size to be a multiple of four
bytes. This seems unnecessary, we can just pad with a few bytes to
get the required alignment.

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

scripts: add tool to create image for SPI boot on AM35xx ...

Booting from SPI on an AM35xx (and possibly other TI SOCs) requires
a special format:

- 32 bit image size in big-endian
- 32 bit load address in big-endian
- binary image converted from little- to big-endian

The mk-am35xx-spi-image tool converts barebox.bin to
this format.

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