[S390] termio <-> termios conversion error handling.

Get rid of our own user_termio_to_kernel_termios() and
kernel_termios_to_user_termio() macros which didn't check for errors
on user space accesses. Instead use the generic functions which
handle this properly.
In addition the generic version of user_termio_to_kernel_termios()
also copies the c_line member which was missing in our variant.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>