toshiba_acpi: Add alternative keymap support for Satellite M840

Toshiba Satellite M840 laptop has a complete different keymap although
it's bound with the same ACPI ID "TOS1900".  This patch provides an
alternative keymap specific to this machine by identifying via DMI
matching.  The keymap table doesn't fill all entries that were used
before since some keys aren't found on this machine at all.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=69761
Bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=812209


Reported-and-tested-by: Federico Vecchiarelli <fedev@gmx.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>