ptp_qoriq: add little enadian support

There is QorIQ 1588 timer IP block on the new ENETC Ethernet
controller. However it uses little endian mode which is different
with before. This patch is to add little endian support for the
driver by using "little-endian" dts node property.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>