net: lib: http: split out URL parsing as a separate CONFIG

With the introduction of CoAP and other protocols, URL parsing is
be needed when HTTP_PARSER is not.  Let's split out the existing
functionality of URL parsing into it's own CONFIG and let
HTTP_PARSER use it by automatically selecting HTTP_PARSER_URL when
HTTP_PARSER is enabled.

Signed-off-by: Michael Scott <michael.scott@linaro.org>