flexcan: Fix up fsl-flexcan device tree binding.

This patch cleans up the documentation of the device-tree binding for
the Flexcan devices on Freescale's PowerPC and ARM cores. Extra
properties are not used by the driver so we are removing them.

Signed-off-by: Robin Holt <holt@sgi.com>
Acked-by: Marc Kleine-Budde <mkl@pengutronix.de>,
Acked-by: Wolfgang Grandegger <wg@grandegger.com>,
Cc: U Bhaskar-B22300 <B22300@freescale.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Kumar Gala <galak@kernel.crashing.org>
Cc: socketcan-core@lists.berlios.de,
Cc: netdev@vger.kernel.org,
Cc: PPC list <linuxppc-dev@lists.ozlabs.org>
Cc: devicetree-discuss@lists.ozlabs.org
Signed-off-by: David S. Miller <davem@davemloft.net>