Log Message:
security/zoneminder: Work around phpversion.mk setting PKG_SYSCONFSUBDIR

phpversion.mk sets PKG_SYSCONFSUBDIR if not set, and that results in
zoneminder's PKG_SYSCONFDIR being e.g. /usr/pkg/etc/php/8.2, leading
to not reading the conf file and mysterious authentication failures.

Work around this by setting PKG_SYSCONFSUBDIR before including
lang/php/phpversion.mk, and then using PKG_SYSCONFDIR instead of
PKG_SYSCONFDIR/zm.  (That's arguably better anyway, separately from it
working around the problem in phpversion.mk.)