btrfs: prepare scrub to support bs > ps cases

This involves:

- Migrate scrub_stripe::pages[] to folios[]

- Use btrfs_alloc_folio_array() and folio_put() to alloc above array.

- Migrate scrub_stripe_get_kaddr() and scrub_stripe_get_paddr() to use
  folio interfaces

- Migrate raid56_parity_cache_data_pages() to
  raid56_parity_cache_data_folios()
  Since scrub is the only caller still using pages.

  This helper will copy the folio array contents into rbio::stripe_pages,
  with sector uptodate flags updated.

  And a new ASSERT() to make sure bs > ps cases will not hit this path.

Since most scrub code is based on kaddr/paddr, the migration itself is
pretty straightforward.

And since we're here, also move the loop to set the
stripe_sectors[].uptodate out of the copy loop.
As we always mark all the sectors as uptodate for the data stripe, it's
easier to do in one go, other than doing it inside the copy loop.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>