staging: iio: ad2s1210: Switch to the gpio descriptor interface.

Use the gpiod interface instead of the deprecated old non-descriptor

Changes in v7:
- Adds a level of indirection to read and write the gpio_desc to make the code simpler.
- Drop gpioin flag which decides how the GPIOs
are controlled as the GPIOs must be outputs
for the host as per the datasheet.
Changes in v6:
- Split device tree table addition and device tree support addition in two patches.
- Replace platform data with device tree support.
- Rename boolean property.
Changes in v5:
- Add device tree support.
- Add device tree table for matching vendor ID.
- Add Support for retrieving platform data from device tree.
Changes in v4:
- Add spaces after { and before } in gpios[] initialization.
- Check the correct pointer for error.
- Align the dev_err msg to existing format in the code.
Changes in v3:
- Use a pointer to pointer for gpio_desc in
struct ad2s1210_gpio as it will be used to modify a pointer.
- Use dot notation to initialize the structure.
- Use a pointer variable to avoid writing gpios[i].
Changes in v2:
- Use the spi_device struct embedded in st instead of passing it as an argument to ad2s1210_setup_gpios().
- Use an array of structs to reduce redundant code in in ad2s1210_setup_gpios().
- Remove ad2s1210_free_gpios() as devm API is being used.

Nishad Kamdar (3):
staging: iio: ad2s1210: Switch to the gpio descriptor interface
staging: iio: ad2s1210: Drop the gpioin flag.
staging: iio: ad2s1210: Add device tree table.

 drivers/staging/iio/resolver/ad2s1210.c | 132 +++++++++++-------------
 drivers/staging/iio/resolver/ad2s1210.h |  20 ----
 2 files changed, 62 insertions(+), 90 deletions(-)

2.17.1