linuxkpi: swap.h: Fix include

Add needed includes so we can use it.

Reviewed by:	bz
Fixes:	c3f4f28c63 ("linuxkpi: Add some basic swap functions")
Sponsored by:	Beckhoff Automation GmbH & Co. KG
Differential Revision:	https://reviews.freebsd.org/D36109

sys/compat/linuxkpi/common/include/linux/swap.h

@@ -29,6 +29,13 @@
 #ifndef	_LINUXKPI_LINUX_SWAP_H_
 #define	_LINUXKPI_LINUX_SWAP_H_
 
+#include <sys/param.h>
+#include <sys/domainset.h>
+#include <sys/queue.h>
+#include <sys/proc.h>
+#include <sys/pcpu.h>
+
+#include <vm/vm.h>
 #include <vm/swap_pager.h>
 #include <vm/vm_pageout.h>