tools: dumpimage: Provide more feedback on internal errors

tools: dumpimage: Provide more feedback on internal errors

The dumpimage utility errors out in a number of places without providing
sufficient feedback to allow the user to easily determine what has gone
wrong. Add additional error messages to make the cause of the failure
more obvious.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>