mm/codetag: uninline and move pgalloc_tag_copy and pgalloc_tag_split

mm/codetag: uninline and move pgalloc_tag_copy and pgalloc_tag_split

pgalloc_tag_copy() and pgalloc_tag_split() are sizable and outside of any
performance-critical paths, so it should be fine to uninline them.  Also
move their declarations into pgalloc_tag.h which seems like a more
appropriate place for them.  No functional changes other than uninlining.

Link: https://lkml.kernel.org/r/20241024162318.1640781-1-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Yu Zhao <yuzhao@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Sourav Panda <souravpanda@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>