Adds more keys to the default virtio keyboard.
Adds more keys to the default virtio keyboard.

These keys are frequently found as hardware keys on mobile devices.

BUG=b:163628929
TEST=Use crosvm to launch AOSP Cuttlefish and send volume key events.

Change-Id: I9175d32cfd4060abd74f0fde4100284483f13102
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2369357
Tested-by: Daniel Norman <55c1efb3a3c3b2e56d9c2f9da8e070c4991cf38a@google.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Daniel Norman <55c1efb3a3c3b2e56d9c2f9da8e070c4991cf38a@google.com>
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Reviewed-by: Jorge Moreira Broche <dbc2f9dc0b0e21f6bd297b0a2dc4733f06f8a572@google.com>

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