gpio: Drop long unused DB8500 GPIO driver

gpio: Drop long unused DB8500 GPIO driver

The original U-Boot port for the ST-Ericsson U8500 SoC was dropped
in commit 68282f55b846 ("arm: Remove unused ST-Ericsson u8500 arch").
Most of the drivers related to the old port were removed, but the
db8500_gpio.c driver was forgotten for some reason. There is no way
to select it and it does not compile anymore because of missing
headers, so let's just remove it.

The new port for U8500 introduced in commit 689088f9dae8
("arm: Add support for ST-Ericsson U8500 SoC") fully embraces the
new Driver Model and device trees where possible, so this is
preparation to add a new, simplified GPIO driver based on DM_GPIO.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>