package/php: add config scan directory option

package/php: add config scan directory option

To support using multiple php configuration files, we pass
--with-config-file-scan-dir=/etc/php.d. This allows to put snippets of
PHP configuration files in /etc/php.d.

For php option details see link at [1].

[1] https://www.php.net/manual/en/configuration.file.php

Signed-off-by: Dan Walkes <danwalkes@trellis-logic.com>
[Thomas: make it unconditional]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>