ASoC: OMAP: ams-delta: drop .set_bias_level callback

This functionality has already been implemented in the cx20442 codec
driver (commit f75a8ff6, "ASoC: cx20442:
add bias control over a platform provided regulator"), no need to keep
it here duplicated.

Once done, remove the no longer used AMS_DELTA_LATCH2_MODEM_NRESET
symbol from the board header file and a call to the regulator_toggle()
helper function from the old API wrapper found in the board file.  While
being at it, simplify the way the modem .pm callback handles the
regulator and drop that helper function and its related consumer setup
completely.

Depends on patches 1/3 and 2/3 for clean apply and keep things working.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>