ARM: OMAP4: MMC: fix power and audio issue, decouple USBC1 from MMC1

ARM: OMAP4: MMC: fix power and audio issue, decouple USBC1 from MMC1

Remove OMAP4_USBC1_ICUSB_PWRDNZ_MASK during enable/disable PWRDNZ mode for
MMC1_PBIAS and associated extended-drain MMC1 I/O cell. This is in accordance
with the control module programming guide. This fixes a bug where if trying to
use gpio_98 or gpio_99 and MMC1 at the same time the GPIO signal will be
affected by a changing SDMMC1_VDDS.

Software must keep MMC1_PBIAS cell and MMC1_IO cell PWRDNZ signals low whenever
SDMMC1_VDDS ramps up/down or changes for cell protection purposes.

MMC1 is based on SDMMC1_VDDS whereas USBC1 is based on SIM_VDDS therefore
they can operate independently.

Signed-off-by: Bryan Buckley <bryan.buckley@ti.com>
Acked-by:  Kishore Kadiyala <kishore.kadiyala@ti.com>
Tested-by: Balaji T K <balajitk@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>