spa: expose utils/cleanup.h for external users

Up until now, spa/utils/cleanup.h was not installed, but 779f0686 ("pod: add spa_auto support for dynamic builder") included it in a public header. So now cleanup.h also needs to be installed like any other public header so as to not break 3rd party users.

For example, xdg-desktop-portal-wlr would break: https://codesearch.debian.net/search?q=spa_pod_dynamic_builder_init&literal=1