mfd: ab8500-core: Use the correct driver name when enabling gpio/pinctrl

When we're using Device Tree to enable GPIO drivers we're forced to be
OS agnostic, thus we are forbidden use names like pinctrl as they are
specific only to Linux, at least for the time being. However, when we
are registering devices using internal systems such as MFD or platform
registration, we can use such terminology. In this case we can and
should use the platform device ID mechanism to specify which device we
wish to utilise by detailing pinctrl-<device_name>.

This patch fixes a regression that when booting with Device Tree
enabled the ABx500 GPIO/Pinctrl devices are not probed.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>