drivers/misc: Aspeed LPC snoop output using misc chardev

Provides the data bytes snooped over the LPC snoop bus to userspace
as a (blocking) misc character device.

Bytes output from the host using LPC I/O transactions to the snooped port
can be watched or retrieved from the character device using a simple
command like this:
~#  od -w1 -A n -t x1 /dev/aspeed-lpc-snoop0
 10
 de
 ad
 c0
 ff
 ee

Signed-off-by: Robert Lippert <rlippert@google.com>
Signed-off-by: Patrick Venture <venture@google.com>
Signed-off-by: Benjamin Fair <benjaminfair@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>