gpio: i8255: Remove unused legacy interface

All i8255 library consumers have migrated to the new interface
leveraging the gpio-regmap API. Legacy interface functions and code are
removed as no longer needed.

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

gpio: i8255: Migrate to gpio-regmap API

The regmap API supports IO port accessors so we can take advantage of
regmap abstractions rather than handling access to the device registers
directly in the driver.

By leveraging the gpio-regmap API, the i8255 library is reduced to
simply a devm_i8255_regmap_register() function, a configuration
structure struct i8255_regmap_config, and a helper macro
i8255_volatile_regmap_range() provided to simplify volatile PPI register
hinting for the regmap.

Legacy functions and code will be removed once all consumers have
migrated to the new i8255 library interface.

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

gpio: i8255: Introduce the Intel 8255 interface library module

Exposes consumer library functions providing support for interfaces
compatible with the venerable Intel 8255 Programmable Peripheral
Interface (PPI).

The Intel 8255 PPI first appeared in the early 1970s, initially for the
Intel 8080 and later appearing in the original IBM-PC. The popularity of
the original Intel 8255 chip led to many subsequent variants and clones
of the interface in various chips and integrated circuits. Although
still popular, interfaces compatible with the Intel 8255 PPI are
nowdays typically found embedded in larger VLSI processing chips and
FPGA components rather than as discrete ICs.

A CONFIG_GPIO_I8255 Kconfig option is introduced by this patch. Modules
wanting access to these i8255 library functions should select this
Kconfig option, and import the I8255 symbol namespace.

Tested-by: Fred Eckert <Frede@cmslaser.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: John Hentges <jhentges@accesio.com>
Cc: Jay Dolan <jay.dolan@accesio.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>