powerpc: dts: fsl: Drop obsolete fsl,rx-bit-map and fsl,tx-bit-map properties

These are very old properties that were used by the "gianfar" ethernet
driver.  They don't have documented bindings and are obsolete.

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>