Add driver for BERI soft processor 'ring buffer' device.
Ring device provides a way for communicate to BERI
peripherals such as BERI debug unit and console.

Sponsored by:	DARPA, AFRL


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273278 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f