Add support for gdb's memory searching capabilities to our in-kernel gdb
server.

Submitted by:	Daniel O'Connor <daniel.oconnor@isilon.com>
Reviewed by:	jhb
Sponsored by:	EMC Isilon Storage Division


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271173 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f