ASoC: sgtl5000: Fix regulator support

Regulator support on SGTL5000 is broken because the VDDIO and
VDDA and VDDD should be powered on before enabling MCLK as
shown in Figure 4 of [1]. This requires moving control of the
regulators from the codec block to the I2C block of the driver.

The bulk of this patch consists of swapping the codec device with
the i2c client. The new field num_supplies in struct sgtl5000_priv
is used instead of ARRAY_SIZE(supplies) to handle the special case
when the internal LDO is used instead of external VDDD.

Note that ER1 in the SGTL5000 Errata document [2] suggests that
all designs should use external VDDD.

Since the internal LDO can only be enabled after I2C is available,
there's no benefit in treating it as a regulator, so this patch
removes the regulator structure surrounding it.

Instead, a single block of code in sgtl5000_i2c_probe() performs
the initialization sequence in section 2.2.1.1 of [3] and page
26 of [1].

References:
[1] SGTL5000 data sheet
    http://cache.nxp.com/files/analog/doc/data_sheet/SGTL5000.pdf
[2] SGTL5000 errata
    http://cache.nxp.com/files/analog/doc/errata/SGTL5000ER.pdf
[3] SGTL5000 Initialization and programming app note
    http://cache.nxp.com/files/analog/doc/app_note/AN3663.pdf

Signed-off-by: Eric Nelson <eric@nelint.com>
Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
Tested-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>