devices: virtio: input: use descriptor reader/writer
devices: virtio: input: use descriptor reader/writer

Convert the virtio input device to use the descriptor_utils
Reader/Writer helpers to simplify the code and allow support of
arbitrary descriptor layouts.

BUG=chromium:966258
TEST=./build_test.py

Change-Id: Ia9272496dc59b29ea9cde9f6454099c881242d4c
Signed-off-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1811712
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Stephen Barber <7719587e4b5a49340661b214ec85602f3918d06f@chromium.org>

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