sgi-xp: move xpc_allocate() into xpc_send()/xpc_send_notify()

Move xpc_allocate() functionality into xpc_send()/xpc_send_notify() so
xpc_allocate() no longer needs to be called by XPNET.

Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>