ec/kontron/kempld: Add minimal GPIO driver

This patch adds an interface for configuring GPIOs inside the Kontron
CPLD/EC. There are several ways to do this: you can enable <ec/kontron/
kempel/kempeld.h> in the source codes with board initialization and
configure/manage each pad using the API or statically define the GPIO
configuration in devicetree.cb. For example:

chip ec/kontron/kempld
	device gpio 0 on
		register "gpio_pad[0]"  = "KEMPLD_PAD_GPIO_CFG_IN"
		register "gpio_pad[4]"  = "KEMPLD_PAD_GPIO_CFG_OUT(1)"
		register "gpio_pad[5]"  = "KEMPLD_PAD_GPIO_CFG_OUT(0)"
	end
end

KEMPLD_PAD_GPIO_CFG_IN     - configure the pad as an input;
KEMPLD_PAD_GPIO_CFG_OUT(1) - configure the pad as an output, set to 1;
KEMPLD_PAD_GPIO_CFG_OUT(0) - configure the pad as an output, set to 0.

The pad configuration is set using the options gpio_pad[], however, if
this option is not set, the corresponding pad will be configured as an
input. In this case, <device gpio 0>, like all other devices, is not a
real device inside the EC. These definitions are used to understand the
EC resources and systematize configuration options, but if mark this as
<off>, the initialization step will be skipped in the driver code.

This work is based on code from the drivers/gpio/gpio-kempld.c linux
driver. Tested on Kontron mAL-10 COMe module CB:54380 .

Change-Id: Id767aa451fbf2ca1c0dccfc9aa2c024c6f37c1bb
Signed-off-by: Maxim Polyakov <max.senia.poliak@gmail.com>
---
M src/ec/kontron/kempld/Makefile.inc
M src/ec/kontron/kempld/chip.h
M src/ec/kontron/kempld/kempld.c
M src/ec/kontron/kempld/kempld.h
A src/ec/kontron/kempld/kempld_gpio.c
M src/ec/kontron/kempld/kempld_internal.h
6 files changed, 133 insertions(+), 1 deletion(-)