[media] rc5x: 6th command bit is S2 bit

The 2nd stop bit in rc5 is reused as an inverted 6th command bit in
20 bits rc5x. Currently the rc5x decoder sets the 6th command bit as
an inverted duplicate of the lowest system bit; as a result we do
not have all the command bits.

Note that there are no rc5x keymaps present.

Signed-off-by: Sean Young <sean@mess.org>
Cc: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>