regulator: fixed: Support for open drain gpio pin

Adding flag on fixed regulator board configuration structure
to specify whether gpio is open drain type or not.
Passing this information to gpio library when requesting
gpio so that gpio driver can set the pin state accordingly,
for open drain type:
- Pin can be set HIGH as setting as input, PULL UP on
  pin make this as HIGH.
- Pin can be set LOW as setting it as output and drive to LOW.

The non-open drain pin can be  set HIGH/LOW by setting it to
output and driving it to HIGH/LOW.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>