Linux 5.9 compat: add linux/blkdev.h include

Many of the block device operations (often functions with bdev in
the name) were moved into linux/blkdev.h from linux/fs.h. Seems
that this header is already included where needed in the code, but
in the autoconf tests it was missing causing false negatives. This
commit has those tests include linux/fs.h (old location) and now
also linux/blkdev.h (new locations).

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #10696
(cherry picked from commit 1823c8fe6a)
Signed-off-by: Eli Schwartz <eschwartz@archlinux.org>

config/kernel-blkdev-get-by-path.m4

@@ -6,6 +6,7 @@ dnl #
 AC_DEFUN([ZFS_AC_KERNEL_SRC_BLKDEV_GET_BY_PATH], [
 	ZFS_LINUX_TEST_SRC([blkdev_get_by_path], [
 		#include <linux/fs.h>
+		#include <linux/blkdev.h>
 	], [
 		blkdev_get_by_path(NULL, 0, NULL);
 	])

config/kernel-blkdev-reread-part.m4

@@ -5,6 +5,7 @@ dnl #
 AC_DEFUN([ZFS_AC_KERNEL_SRC_BLKDEV_REREAD_PART], [
 	ZFS_LINUX_TEST_SRC([blkdev_reread_part], [
 		#include <linux/fs.h>
+		#include <linux/blkdev.h>
 	], [
 		struct block_device *bdev = NULL;
 		int error;

config/kernel-invalidate-bdev-args.m4

@@ -5,6 +5,7 @@ dnl #
 AC_DEFUN([ZFS_AC_KERNEL_SRC_INVALIDATE_BDEV], [
 	ZFS_LINUX_TEST_SRC([invalidate_bdev], [
 		#include <linux/buffer_head.h>
+		#include <linux/blkdev.h>
 	],[
 		struct block_device *bdev = NULL;
 		invalidate_bdev(bdev);

config/kernel-lookup-bdev.m4

@@ -5,6 +5,7 @@ dnl #
 AC_DEFUN([ZFS_AC_KERNEL_SRC_LOOKUP_BDEV], [
 	ZFS_LINUX_TEST_SRC([lookup_bdev_1arg], [
 		#include <linux/fs.h>
+		#include <linux/blkdev.h>
 	], [
 		lookup_bdev(NULL);
 	])