USB: add arrow key support to usb_kbd

Check for scancodes for arrow keys and map them to ^F/^B, ^N/^P.
Control characters are used instead of ANSI sequence because the
queueing code in usb_kbd doesn't handle the data increase when one
keypress generates 3 keycodes.  The real fix is to convert this driver
to use the input subsystem and queue, but this allows arrow keys to
work until this driver is converted.

Signed-off-by: Allen Martin <amartin@nvidia.com>