docbook-dsssl-stylesheets-native_1.79.bb: converted to new style staging

docbook-dsssl-stylesheets-native_1.79.bb: converted to new style staging

* Converted do_stage to do_install.
* Moved the catalog files from ${sysconfdir}/sgml to ${D}${sysconfdir}/sgml so that they get included in the package file resulting with the new style staging.
* Added a function docbook_dssl_stylesheets_native_mangle, to correct the path in .cat file and added it to SYSROOT_PREPROCESS_FUNCS.
* Added PR = "r1"

Signed-off-by: Fahad Usman <fahad_usman@mentor.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>