openssl_1.0: add PACKAGECONFIG option to control manpages

openssl_1.0: add PACKAGECONFIG option to control manpages

Creating the openssl manpages, which happens as part of do_install(),
can take a significant amount of time (e.g. ~50 seconds on a quad
core laptop). Provide a PACKAGECONFIG option to allow creation of the
manpages to be skipped completely if not required and inherit the
manpages class to automatically control the PACKAGECONFIG option
(based on the "api-documentation" distro feature).

Signed-off-by: Andre McCurdy <armccurdy@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>