gpio: Add support for the Xylon LogiCVC GPIOs

The LogiCVC display hardware block comes with GPIO capabilities
that must be exposed separately from the main driver (as GPIOs) for
use with regulators and panels. A syscon is used to share the same
regmap across the two drivers.

Add a minimalistic GPIO driver to drive these GPIOs, using a syscon
regmap when available.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Link: https://lore.kernel.org/r/20191203141243.251058-5-paul.kocialkowski@bootlin.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Kconfig

@@ -312,6 +312,12 @@ config GPIO_IXP4XX
 	  IXP4xx series of chips.
 
 	  If unsure, say N.
+config GPIO_LOGICVC
+	tristate "Xylon LogiCVC GPIO support"
+	depends on MFD_SYSCON && OF
+	help
+	  Say yes here to support GPIO functionality of the Xylon LogiCVC
+	  programmable logic block.
 
 config GPIO_LOONGSON
 	bool "Loongson-2/3 GPIO support"