dev_pager: define free_page for mgt devices

[dougm]

Summary

Callers of cdev_pager_free_page always have object->type == OBJT_MGTDEVICE. Define a function for them to call that skips the runtime type check.

[kib]

sys/vm/device_pager.c

264–265

I do not see much reason to keep this assert, both callees are asserting the same lock.

275

I suggest to keep the cdev_ name prefix. Like cdev_mgtdev_pager_free_page()

[dougm]

Accept all suggestions.