devices: block: report block size in config
devices: block: report block size in config

Set up the infrastructure for reporting block size in the virtio-blk
device model.  For now, we'll keep reporting SECTOR_SIZE (512), which is
the default block size that is assumed if we don't report it.  This
prepares us to easily switch the reported block size in the future.

BUG=chromium:942700
TEST=Boot Crostini on nami with an existing VM and container

Change-Id: I983817743c40e8278fe6cb9a10498011a8887ec9
Signed-off-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1526334
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>

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