mfd: ab8500-gpadc: Make it explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/mfd/Kconfig:config AB8500_GPADC
drivers/mfd/Kconfig:    bool "ST-Ericsson AB8500 GPADC 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 in use by this code, the init ordering
remains unchanged with this commit.

We also delete the MODULE_LICENSE tag etc. since all that information
was (or is now) contained at the top of the file in the comments.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>