Backport two io-wq fixes relevant for io_uring

Backport two io-wq fixes relevant for io_uring

There were quite a few reports in the community forum about Windows
VMs with SATA disks not working after upgrading to kernel 5.13.
Issue was reproducible during the installation of Win2019 (suggested
by Thomas), and it's already fixed in 5.15. Bisecting led to
    io-wq: split bounded and unbounded work into separate lists
as the commit fixing the issue.

Indeed, the commit states
    Fixes: ecc53c48c13d ("io-wq: check max_worker limits if a worker transitions bound state")
which is present as a backport in ubuntu-impish:
    f9eb79f840052285408ae9082dc4419dc1397954

The first backport
    io-wq: fix queue stalling race
also sounds nice to have and additionally served as a preparation for
the second one to apply more cleanly.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>