MIPS: Loongson: Make platform serial setup always built-in.

MIPS: Loongson: Make platform serial setup always built-in.

commit 26927f76499849e095714452b8a4e09350f6a3b9 upstream.

If SERIAL_8250 is compiled as a module, the platform specific setup
for Loongson will be a module too, and it will not work very well.
At least on Loongson 3 it will trigger a build failure,
since loongson_sysconf is not exported to modules.

Fix by making the platform specific serial code always built-in.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Reported-by: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Markos Chandras <Markos.Chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/8533/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>