mfd: max77620: Make it explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/mfd/Kconfig:config MFD_MAX77620
drivers/mfd/Kconfig:    bool "Maxim Semiconductor MAX77620 and MAX20024 PMIC Support"

...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_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
was (or is now) contained at the top of the file in the comments.

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