[package] php5: first steps to simplify the Makefile

[package] php5: first steps to simplify the Makefile

- Introduce /etc/php5 which is scanned for additional configuration files.
  So it is possible that a installed modules is automatically enabled
  without the need to modify the php.ini.
- Remove unsupported config option: --disable-ttf
- Add support for SimpleXML module, closes #7758.
- Add support for PCNTL module.
- Modularize System V stuff.
- Rename BuildPlugin to BuildModule which IMHO fits better to the
  commonly used terminology of "PHP module".

Signed-off-by: Michael Heimpold <mhei@heimpold.de>
git-svn-id: svn://svn.openwrt.org/openwrt/packages@25673 3c298f89-4303-0410-b956-a3cf2f4a3e73