drivers/tty: make serial/sn_console.c driver explicitly non-modular

The Kconfig for this option is currently:

config SERIAL_SGI_L1_CONSOLE
    bool "SGI Altix L1 serial console support"

...meaning that it currently is not being built as a module by anyone.
Lets remove the orphaned module code, so that when reading the
driver there is no doubt it is builtin-only.  We could consider
making it tristate, but the above bool has been there since before
the start of git history, which isn't all that surprising, since
consoles are typically critical to have at early boot.  So adding
tristate is really of no value here.

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

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>