ar71xx: add mask and shift for RXD/RDV bits in AR934X register file

ar71xx: add mask and shift for RXD/RDV bits in AR934X register file

The commit r38948 ("ag71xx: add F1E specific feature bit definitions to AR934X
register file") introduced definitions for some bits in the RDV/RXD part of the
ETH_CFG register of AR934x. These are incomplete because ETH_RXDV_DELAY is
specified as 17:16 and ETH_RXD_DELAY is specified 15:14. The original commit
only specified the lower bits. The upper bits also have to be unset when the
lower bits should only be set.

Signed-off-by: Sven Eckelmann <sven@open-mesh.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45522 3c298f89-4303-0410-b956-a3cf2f4a3e73