ANDROID: mm: export symbols used in vendor hook android_vh_get_swap_page()

3 symbols are exported to be used in vendor hook android_vh_get_swap_page:
1)check_cache_active, used to get swap page from the specified
swap location, it's usage is similar to the usage in get_swap_page
2)scan_swap_map_slots, used to get swap page from the specified swap,
it's usage is similar to get_swap_pages
3)swap_alloc_cluster, used to get swap page from the specified swap,
it's usage is similar to get_swap_pages

Bug: 234214858
Signed-off-by: Bing Han <bing.han@transsion.com>
Change-Id: Ie24c5d32a16c7cb87905d034095ec8fb070dbe0f