Fix scancodes returned by driver to match scancodes used to remap keys.

(Before the patch FN/E returned scancode 0x1B, but to remap scancode
0x14 had to be used).

The scancodes returned by the sony-laptop driver for function keys did not
match the scancodes used to remap keys.  Also, since the scancode was sent
to the input subsystem after the mapped keysym the /lib/udev/keymap
utility was confused about which scancode to report for which keysym.

This patch fixes the driver so the correct scancode is shown for each
key.  It also adds to the documentation a description of where to find
the scancodes.
Signed-off-by: John Hughes <john@calva.com>
Acked-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Matthew Garrett <mjg@redhat.com>