PKG_OPTIONS change for PHP packages

[Takahiro Kambe]

Hi,

Along with updating of php54 to 5.4.29 and php55 to 5.5.13, I changed
setting of PKG_OPTIONS_VAR in lang/php5{3,4,5}/Makefile.php.

Previously, it was set to the same value as ${PKGBASE} and now it is
set to PKG_OPTIONS.${PHP_PKG_PREFIX}, such as PKG_OPTIONS.php54.

It make setting of PKG_OPTIONS consistent among with packages which
use lang/php5{3,4,5}/Makefile.php. For example, lang/php54 and
www/ap-php are always the same PKG_OPTIONS setting.

Best regards.