TSEC: add config options for VSC8601 RGMII PHY

The Vitesse VSC8601 RGMII PHY has internal delay for both Rx
and Tx clock lines. They are configured using 2 bits in extended
register 0x17.
Therefore CFG_VSC8601_SKEW_TX and CFG_VSC8601_SKEW_RX have
been introduced with valid values 0-3 giving 0.0, 1.4,1.7 and 2.0ns delay.

Signed-off-by: Andre Schwarz <andre.schwarz@matrix-vision.de>
Acked-by: Andy Fleming <afleming@freescale.com>
Acked-by: Ben Warren <biggerbadderben@gmail.com>
--

 drivers/net/tsec.c |    6 ++++++
 drivers/net/tsec.h |    3 +++
 2 files changed, 9 insertions(+), 0 deletions(-)