tty: serial: make crisv10 explicitly non-modular

The Kconfig currently controlling compilation of this code is:

arch/cris/arch-v10/drivers/Kconfig:config ETRAX_SERIAL
arch/cris/arch-v10/drivers/Kconfig:     bool "Serial-port support"

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

Lets remove the couple traces of modular infrastructure use, so that
when reading the driver there is no doubt it is builtin-only.

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

We don't replace module.h with init.h since the file already has that.

Cc: Mikael Starvik <starvik@axis.com>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-cris-kernel@axis.com
Cc: linux-serial@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jesper Nilsson <jespern@axis.com>