parisc/serial: Rename 8250_gsc.c to 8250_parisc.c

The file name of this driver is misleading - it handles various serial
ports on parisc machines, not just such on the GSC bus.
Rename the file to make this clearer.

Suggested-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Helge Deller <deller@gmx.de>