serial: pxa: make it explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/tty/serial/Kconfig:config SERIAL_PXA
drivers/tty/serial/Kconfig:     bool "PXA serial port 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.

We explicitly disallow a driver unbind, since that doesn't have a
sensible use case anyway, and it allows us to drop the ".remove"
code for non-modular drivers.

Since module_init translates to device_initcall in the non-modular
case, the init ordering remains unchanged with this commit.

Also note that MODULE_DEVICE_TABLE and MODULE_ALIAS are both a
no-op for non-modular builds.

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

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-serial@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>