ARM: keystone2: Add support for parsing monitor header

ARM: keystone2: Add support for parsing monitor header

Given that boot monitor image is being generated to a specific target location
depending on the SoC and U-boot relies on addr_mon env variable to be aligned
with boot monitor target location. When ever the target address gets updated in
boot monitor, it is difficult to sync between u-boot and boot monitor and also
there is no way to update user that boot monitor image is updated.

To avoid this problem, boot monitor image is being generated with mkimage
header. Adding support in mon_install command for parsing this header.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>