pinctrl: at91: make it explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/pinctrl/Kconfig:config PINCTRL_AT91
drivers/pinctrl/Kconfig:        bool "AT91 pinctrl 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.

Since module_init was not being used in this driver, we don't need
to be concerned with initcall ordering changes when removing it.

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: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>