gpio: Remove GPIO_DEVRES option

gpio: Remove GPIO_DEVRES option

This option was added in 6a89a314ab107a12af08c71420c19a37a30fc2d3 to
allow use of the devm_gpio_* functions without CONFIG_GPIOLIB.

However, only a few months later in
b69ac52449c658b7ac40034dc3c5f5f4a71a723d, CONFIG_GPIOLIB was added
as a dependency, defeating the original purpose of this option.
Instead of that patch, the original commit could have just been
reverted (and in fact was partially so in
403c1d0be5ccbd750d25c59d8358843a81e52e3b). Further, since this
option has a dependency on HAS_IOMEM, even though it does not
require it, it causes build failures when !HAS_IOMEM (e.g. in a
uml build).

Fix that by completely removing the option, in essence completing
the reversion of the original commit.

Signed-off-by: Keno Fischer <keno@juliacomputing.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>