pinctrl: make artpec6 explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/pinctrl/Kconfig:config PINCTRL_ARTPEC6
drivers/pinctrl/Kconfig:        bool "Axis ARTPEC-6 pin controller driver"

...meaning that it currently is not being built as a module by anyone.

Lets remove the modular code that is essentially orphaned, so that
when reading the driver there is no doubt it is builtin-only.

Also note that MODULE_DEVICE_TABLE is a no-op for non-modular code.

We also delete the MODULE_LICENSE tag etc. since all that information
is already contained at the top of the file in the comments.

Cc: Lars Persson <lars.persson@axis.com>
Cc: Niklas Cassel <niklas.cassel@axis.com>
Cc: linux-arm-kernel@axis.com
Cc: linux-gpio@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Jesper Nilsson <jesper.nilsson@axis.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>