x86: convert termios.h to the asm-generic version

This patch turned out more controversial than expected
and may get dropped in the future. I'm including it
for reference anyway.

The user_termio_to_kernel_termios and kernel_termios_to_user_termio
functions on x86 are lacking error checking from get_user and
are not portable to big-endian systems, so the asm-generic
header has to differ in this regard.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
LKML-Reference: <cover.1245354003.git.arnd@arndb.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>