disable loading f2fs module on PAGE_SIZE > 4KB

The following patch disables loading of f2fs module on architectures
which have PAGE_SIZE > 4096 , since it is impossible to mount f2fs on
such architectures , log messages are:

mount: /mnt: wrong fs type, bad option, bad superblock on
/dev/vdiskb1, missing codepage or helper program, or other error.
/dev/vdiskb1: F2FS filesystem,
UUID=1d8b9ca4-2389-4910-af3b-10998969f09c, volume name ""

May 15 18:03:13 ttip kernel: F2FS-fs (vdiskb1): Invalid
page_cache_size (8192), supports only 4KB
May 15 18:03:13 ttip kernel: F2FS-fs (vdiskb1): Can't find valid F2FS
filesystem in 1th superblock
May 15 18:03:13 ttip kernel: F2FS-fs (vdiskb1): Invalid
page_cache_size (8192), supports only 4KB
May 15 18:03:13 ttip kernel: F2FS-fs (vdiskb1): Can't find valid F2FS
filesystem in 2th superblock
May 15 18:03:13 ttip kernel: F2FS-fs (vdiskb1): Invalid
page_cache_size (8192), supports only 4KB

which was introduced by git commit 5c9b469

tested on git kernel 4.17.0-rc6-00309-gec30dcf7f425

with patch applied:

modprobe: ERROR: could not insert 'f2fs': Invalid argument
May 28 01:40:28 v215 kernel: F2FS not supported on PAGE_SIZE(8192) != 4096

Signed-off-by: Anatoly Pugachev <[email protected]>
Reviewed-by: Chao Yu <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>

fs/f2fs/super.c

@@ -3122,6 +3122,12 @@ static int __init init_f2fs_fs(void)
 {
 	int err;
 
+	if (PAGE_SIZE != F2FS_BLKSIZE) {
+		printk("F2FS not supported on PAGE_SIZE(%lu) != %d\n",
+				PAGE_SIZE, F2FS_BLKSIZE);
+		return -EINVAL;
+	}
+
 	f2fs_build_trace_ios();
 
 	err = init_inodecache();