trivial: Small fixups from compiler warnings

- Use correct printf format strings
- Remove unused symbols
- Move variable initializations around to avoid uninitialized usages
- Add missing const modifiers
- Correct slightly invalid type definitions
- Remove unsupported attribute: force

libvirtqueue: Set queue size on initialization

A virtqueue's queue size specifies the length of each ring and the
length of the descriptor table.

libvirtqueue: Remove volatile qualifier

We do not need to restrict the compiler's behavior in this way.

Avoid warning about pointer/integer casting

Added new libvirtqueue

Created a new multi-buffer, scatter-gather libvirtqueue, closer to
compliance with the virtio standard.

Removed old deprecated libvirtqueue

Removed the old single-buffer libvirtqueue as a preliminary commit for
introducing the new one.

libvirtqueue: Avoid setting header flags on init

Removed the setting of shared header flags in virtqueue
driver/device init. This makes it the callers reponsibility to
initialise and zero the header region before passing it into
virtqueue init. Keeping it otherwise leaves a potential race
condition in the virtqueue library.

virtqueue,vswitch: astyle

virtqueue: s/drv/driver/g s/dev/device/g

virtqueue: astyle

virtqueue: Use consistent function naming scheme

libvirtqueue: Refactor interface into split

This splits the interface into the virtqueue_device_t and
virtqueue_driver_t roles to make using the interface clearer

virtqueue: Added virtqueue library implementation

Added the libvirtqueue library implementation. This is an
initial/basic library that implements a generic virtqueue API,
inspired by virtio communication mechanisms.