treewide: fix licence typos

treewide: fix licence typos

- PKG_LICENCE -> PKG_LICENSE
- PKC_LICENSE_FILES -> PKG_LICENSE_FILES
- BSD 3-Clause -> BSD-3-Clause
- BSD-3-clause -> BSD-3-Clause
- BSD-2-clause -> BSD-2-Clause
- Public Domain -> Public-Domain
- PublicDomain -> Public-Domain
- Drop unneeded ',' in PKG_LICENSE or PKG_LICENSE_FILES

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>