ASoC: change set_tdm_slot api to allow slot_width override.

Extend set_tdm_slot to allow the user to arbitrarily set the frame width
and active TX/RX slots.

Updates magician.c and wm9081.c for the new set_tdm_slot(). wm9081.c
still doesn't handle the slot_width override.

While being there, correct an incorrect use of SlotsPerFrm(7) use in
bitmask on pxa-ssp.c (SSCR0_SlotsPerFrm(x) is (((x) - 1) << 24)) ).

(this series is meant for Mark's for-2.6.32 branch)

Signed-off-by: Daniel Ribeiro <drwyrm@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>