page_pool: split types and declarations from page_pool.h

Split types and pure function declarations from page_pool.h
and add them in page_page/types.h, so that C sources can
include page_pool.h and headers should generally only include
page_pool/types.h as suggested by jakub.
Rename page_pool.h to page_pool/helpers.h to have both in
one place.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Link: https://lore.kernel.org/r/20230804180529.2483231-2-aleksander.lobakin@intel.com
[Jakub: change microsoft/mana, fix kdoc paths in Documentation]
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c

@@ -2,6 +2,7 @@
 
 #include <linux/bpf.h>
 #include <linux/filter.h>
+#include <net/page_pool/helpers.h>
 
 #include "lan966x_main.h"
 

drivers/net/ethernet/microchip/lan966x/lan966x_main.h

@@ -10,7 +10,7 @@
 #include <linux/phy.h>
 #include <linux/phylink.h>
 #include <linux/ptp_clock_kernel.h>
-#include <net/page_pool.h>
+#include <net/page_pool/types.h>
 #include <net/pkt_cls.h>
 #include <net/pkt_sched.h>
 #include <net/switchdev.h>