Merge remote-tracking branch 'remotes/aperard/tags/pull-xen-20210510' into staging

Xen patches

- Avoid mmap race involving Xen's mapcache
- Fix xenforeignmemory_resource leak at exit
- Fix xen-block to choose a driver for the disk image when created via
  xenstore.

# gpg: Signature made Mon 10 May 2021 13:49:40 BST
# gpg:                using RSA key F80C006308E22CFD8A92E7980CF5572FD7FB55AF
# gpg: Good signature from "Anthony PERARD <anthony.perard@gmail.com>" [unknown]
# gpg:                 aka "Anthony PERARD <anthony.perard@citrix.com>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 5379 2F71 024C 600F 778A  7161 D8D5 7199 DF83 42C8
#      Subkey fingerprint: F80C 0063 08E2 2CFD 8A92  E798 0CF5 572F D7FB 55AF

* remotes/aperard/tags/pull-xen-20210510:
  xen-block: Use specific blockdev driver
  xen: Free xenforeignmemory_resource at exit
  xen-mapcache: avoid a race on memory map while using MAP_FIXED

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>