In order to boot elfs files, add bootm command support for kvx. This support
can boot elf files using bootm elf support. initrd and device-tree handling
is also included and loads them after the elf file load address.

Signed-off-by: Clement Leger <cleger@kalray.eu>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>