MIPS: Remove all the uses of custom gpio.h

MIPS: Remove all the uses of custom gpio.h

Currently CONFIG_ARCH_HAVE_CUSTOM_GPIO_H is defined for all MIPS
machines, and each machine type provides its own gpio.h. However
only a handful really implement the GPIO API, most just forward
everythings to gpiolib.

The Alchemy machine is notable as it provides a system to allow
implementing the GPIO API at the board level. But it is not used by
any board currently supported, so it can also be removed.

For most machine types we can just remove the custom gpio.h, as well
as the custom wrappers if some exists. Some of the code found in
the wrappers must be moved to the respective GPIO driver.

A few more fixes are need in some drivers as they rely on linux/gpio.h
to provides some machine specific definitions, or used asm/gpio.h
instead of linux/gpio.h for the gpio API.

Signed-off-by: Alban Bedel <albeu@free.fr>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-mips@linux-mips.org
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Cc: Rafał Miłecki <zajec5@gmail.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Florian Fainelli <florian@openwrt.org>
Cc: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Daniel Walter <dwalter@google.com>
Cc: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: James Hartley <james.hartley@imgtec.com>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Wolfram Sang <wsa@the-dreams.de>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Varka Bhadram <varkabhadram@gmail.com>
Cc: Masanari Iida <standby24x7@gmail.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Michael Buesch <m@bues.ch>
Cc: abdoulaye berthe <berthe.ab@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-ide@vger.kernel.org
Cc: linux-gpio@vger.kernel.org
Cc: linux-input@vger.kernel.org
Cc: netdev@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/10828/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>