ARM: mxs: tools: Add mkimage support for MXS bootstream

Add mkimage support for generating and verifying MXS bootstream.
The implementation here is mostly a glue code between MXSSB v0.4
and mkimage, but the long-term goal is to rectify this and merge
MXSSB with mkimage more tightly. Once this code is properly in
U-Boot, MXSSB shall be deprecated in favor of mkimage-mxsimage
support.

Note that the mxsimage generator needs libcrypto from OpenSSL, I
therefore enabled the libcrypto/libssl unconditionally.

MXSSB: http://git.denx.de/?p=mxssb.git;a=summary

The code is based on research presented at:
http://www.rockbox.org/wiki/SbFileFormat



Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Otavio Salvador <otavio@ossystems.com.br>