tty: serial: ifx6x60: Convert to GPIO descriptors

This driver for the Intel MID never seems to have been properly
integrated upstream: the platform data in <linux/spi/ifx_modem.h>
is not used anywhere in the kernel and haven't been since it was
merged into the kernel in 2010.

There might be out-of-tree users, so I don't want to delete the
driver, but I will refactor it to use GPIO descriptors, which
means that out-of-tree users will need to adapt.

There are several examples in the kernel of how to provide the
resources necessary for using GPIO descriptors to pass in the
GPIO lines, for the MID platform in particular, it will suffice
to inspect the code in files like:
arch/x86/platform/intel-mid/device_libs/platform_bt.c

This refactoring transfers all GPIOs in the driver, including
a hard-coded "PMU reset" in the driver to use GPIO descriptors
instead.

The following named GPIO descriptors need to be supplied:
- reset
- power
- mrdy
- srdy
- rst_out
- pmu_reset

Cc: Russ Gorby <russ.gorby@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200311083131.693908-2-linus.walleij@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>