drivers/sgi-xp: Convert timers to use timer_setup()

In preparation for unconditionally passing the struct timer_list pointer to
all timer callbacks, switch to using the new timer_setup() and from_timer()
to pass the timer pointer explicitly.

Cc: Cliff Whickman <cpw@sgi.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Robin Holt <robinmholt@gmail.com>