Support providing some IC specific operations at gpio_regmap registration.

Implementation of few GPIO related functionalities are likely to be
very IC specific. For example the pin-configuration registers and the
pin validity checks. Allow IC driver to provide IC specific functions
which gpio-regmap can utilize for these IC specific configurations.
This should help broaden the gpio-regmap IC coverage without the need
of exposing the registered gpio_chip or struct gpio_regmap to IC drivers.

The set_config and init_valid_mask are used by ROHM BD71815 GPIO driver.
Convert the BD71815 GPIO driver to use gpio-regmap and get rid of some
code. Rest of the ROHM GPIO drivers are to be reworked after the
mechanism of adding IC specific functions is settled.

Some preliminary discussion can be seen here:
https://lore.kernel.org/linux-gpio/c4faac648d3e0c7f3dcb50f7e24c8b322e8c6974.camel@fi.rohmeurope.com/

Changelog v2:
 - Add cover-letter
 - Drop unnecessary checks for callback function validity
 - drop driver_data setting function as it is likely to be a
   race-condition-by-design

---

Matti Vaittinen (3):
  gpio: regmap: Support few IC specific operations
  gpio: gpio-regmap: Use devm_add_action()
  gpio: bd71815: Use gpio-regmap

 drivers/gpio/Kconfig        |   1 +
 drivers/gpio/gpio-bd71815.c | 106 ++++++++++--------------------------
 drivers/gpio/gpio-regmap.c  |  62 ++++++++++++++-------
 include/linux/gpio/regmap.h |  14 ++++-
 4 files changed, 84 insertions(+), 99 deletions(-)


base-commit: d07f6ca923ea0927a1024dfccafc5b53b61cfecc
-- 
2.25.4


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =]