staging: nvec: rework the nvec slave init

Rework the tegra slave controller init to look more like in
tegra-i2c.c. This makes the nvec init reliable. Also add de-init of
the slave to be used during suspend.

Signed-off-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Julian Andres Klode <jak@jak-linux.org>
Acked-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>