um: Rename _PAGE_NEWPAGE to _PAGE_NEEDSYNC

The _PAGE_NEWPAGE bit does not really indicate that this is a new page,
but rather whether this entry needs to be synced or not. Renaming it
to _PAGE_NEEDSYNC will make it more clear how everything ties together.

Suggested-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20241011102354.1682626-3-tiwei.btw@antgroup.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>