PPP: add default configuration file and fix hard-coded CFLAGS

PPP: add default configuration file and fix hard-coded CFLAGS

1. Add three ppp configuration files, make "/etc/init.d/ppp start"
be able to work with little change. provider and pap are adopted from
Ubuntu. ppp_on_boot is adopted from http://www.wlug.org.nz.
2. Use build system CFLAGS when compiling

(From OE-Core rev: 6ab8adf980f90040d3a24dd9c0f12dc04d7aadeb)

Signed-off-by: Roy.Li <rongqing.li@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>