pinctrl: adi2: Fix Kconfig build problem

The build robot is complaining on Blackfin:

drivers/pinctrl/pinctrl-adi2.c: In function 'port_setup':
>> drivers/pinctrl/pinctrl-adi2.c:221:21: error: dereferencing
   pointer to incomplete type 'struct gpio_port_t'
      writew(readw(&regs->port_fer) & ~BIT(offset),
                        ^~
drivers/pinctrl/pinctrl-adi2.c: In function 'adi_gpio_ack_irq':
>> drivers/pinctrl/pinctrl-adi2.c:266:18: error: dereferencing
pointer to incomplete type 'struct bfin_pint_regs'
      if (readl(&regs->invert_set) & pintbit)
                     ^~
It seems the driver need to include <asm/gpio.h> and <asm/irq.h>
to compile.

The Blackfin architecture was re-defining the Kconfig
PINCTRL symbol which is not OK, so replaced this with
PINCTRL_BLACKFIN_ADI2 which selects PINCTRL and PINCTRL_ADI2
just like most arches do.

Further, the old GPIO driver symbol GPIO_ADI was possible to
select at the same time as selecting PINCTRL. This was not
working because the arch-local <asm/gpio.h> header contains
an explicit #ifndef PINCTRL clause making compilation break
if you combine them. The same is true for DEBUG_MMRS.

Make sure the ADI2 pinctrl driver is not selected at the same
time as the old GPIO implementation. (This should be converted
to use gpiolib or pincontrol and move to drivers/...) Also make
sure the old GPIO_ADI driver or DEBUG_MMRS is not selected at
the same time as the new PINCTRL implementation, and only make
PINCTRL_ADI2 selectable for the Blackfin families that actually
have it.

This way it is still possible to add e.g. I2C-based pin
control expanders on the Blackfin.

Cc: Steven Miao <realmz6@gmail.com>
Cc: Huanhuan Feng <huanhuan.feng@analog.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>