serial: 8250: export RSA functions

serial: 8250: export RSA functions

The RSA functions moved by the below commit to 8250_rsa.c are used in
8250_base.c. Since that can be a module (when CONFIG_SERIAL_8250=m),
this causes build failures:
  ERROR: modpost: "rsa_autoconfig" [drivers/tty/serial/8250/8250_base.ko] undefined!
  ERROR: modpost: "rsa_reset" [drivers/tty/serial/8250/8250_base.ko] undefined!
  ERROR: modpost: "rsa_disable" [drivers/tty/serial/8250/8250_base.ko] undefined!
  ERROR: modpost: "rsa_enable" [drivers/tty/serial/8250/8250_base.ko] undefined!

Fix them by exporting the functions. But only to the base module using
EXPORT_SYMBOL_GPL_FOR_MODULES(). (And not to the whole world.)

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/all/20250619165607.33403e19@canb.auug.org.au/
Fixes: 5a128fb475fb ("serial: 8250: move RSA functions to 8250_rsa.c")
Link: https://lore.kernel.org/r/20250623061035.436414-1-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>