libweave: Pass firmware using weave::Settings

Also removed unused weave::Options fields.

BUG=brillo:1257
TEST=`FEATURES=test emerge-gizmo libweave buffet`

Change-Id: I9299e3d2f58e9b8f2965cb2198107e865dabb953
Reviewed-on: https://chromium-review.googlesource.com/293927
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>