mfd: twl-core: Make it explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/mfd/Kconfig:config TWL4030_CORE
drivers/mfd/Kconfig:    bool "TI TWL4030/TWL5030/TWL6030/TPS659x0 Support"

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

Lets remove what modular code that we can, so that when reading the
driver there is less doubt that it is builtin-only.  Note that we can't
remove the twl_remove() itself ; it is still used by the probe unwind
routine.  So we leave it linked into the .remove as well, even though
it will most likely never be called via that path from an unbind.

Since module_i2c_driver() uses the same init level priority as
builtin_i2c_driver() the init ordering remains unchanged with
this commit.

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.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>