Implement shm drivers.

Planned drivers are noop, dmabuf and virtwl.

- virtwl will be used by default if /dev/wl0 exists.
- dmabuf will be used by default if drm device was specified.

Specific driver can be forced using --shm-driver flag and
XWL_SHM_DRIVER variable.

Noop driver will just forward shm segments to host

Virtwl and dmabuf driver will allocate shadow buffers and
copy damaged areas into these buffers.
2 files changed