OpenZFS 8067 - zdb should be able to dump literal embedded block pointer

OpenZFS 8067 - zdb should be able to dump literal embedded block pointer

Authored by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Alex Reece <alex@delphix.com>
Reviewed by: Yuri Pankov <yuri.pankov@gmail.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>
OpenZFS-issue: https://www.illumos.org/issues/8067
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/8173085
Closes #6319