btrfs/194: allow it to be run on systems with page size larger than 4K

btrfs/194: allow it to be run on systems with page size larger than 4K

Since btrfs has subpage support since v5.15, there is no need to
require such hard requirement on 4K page size.

We only need to check if the current system support 4K as
sectorsize.

Now the test case can pass on aarch64 with 64K page size.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>