base.bbclass: Implement PACKAGECONFIG

base.bbclass: Implement PACKAGECONFIG

These enabled options to be specified in the form:

PACKAGECONFIG ?? = "<default options>"
PACKAGECONFIG[foo] = "--enable-foo,--disable-foo,foo_depends,foo_runtime_depends"

So that DEPENDS, RDEPENDS_${PN} and EXTRA_OECONF can be automatically
built from specific options. Those options can easily be customised
by the distro config or the user.

Based on some ideas from Chris Elston <celston@katalix.com> but with
an improved easier to use one line interface.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>