io_uring: expand poll_events to 32 bits
io_uring: expand poll_events to 32 bits

The original poll_events field in io_uring_sqe was 16 bits wide, but it
was later extended to 32 bits to allow the use of all epoll flags.

Technically, we should check for the IORING_FEAT_POLL_32BITS feature,
but the new poll32_events union member was added in Linux commit
5769a351b89c ("io_uring: change the poll type to be 32-bits"), which was
included in Linux 5.9, so we can assume this is available for all
io_uring-enabled kernels due to our baseline version of 5.10.

BUG=None
TEST=cargo test -p io_uring

Change-Id: I5a6266f24ba53a1826b40c91c281527481e99c8a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3687056
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Reviewed-by: Anton Romanov <7c8c28e1283c1d87f2c3df4d6b5c74b6ae02bcd9@google.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm