virtio: blk: introduce virtio-block erase support

virtio: blk: introduce virtio-block erase support

Co-developed-by: Cody Schuffelen <schuffelen@google.com>
Signed-off-by: Cody Schuffelen <schuffelen@google.com>
Signed-off-by: Dmitrii Merkurev <dimorinny@google.com>
Cc: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Cc: Simon Glass <sjg@chromium.org>
Cc: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Cc: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # sandbox