The fec/enet driver calculates MDC rate with the formula below.

  ref_freq / ((MII_SPEED + 1) x 2)

The ref_freq here is the fec internal module clock, which is missing
from clk-vf610 clock driver right now.  And clk-vf610 driver mistakenly
supplies RMII clock (50 MHz) as the source to fec.  This results in the
situation that fec driver gets ref_freq as 50 MHz, while physically it
runs at 66 MHz (fec module clock physically sources from ipg which runs
at 66 MHz).  That's why software expects MDC runs at 2.5 MHz, while the
measurement tells it runs at 3.3 MHz.  And this causes the PHY KSZ8041
keeps swithing between Full and Half mode as below.

  libphy: 400d0000.etherne:00 - Link is Up - 100/Full
  libphy: 400d0000.etherne:00 - Link is Up - 100/Half
  libphy: 400d0000.etherne:00 - Link is Up - 100/Full
  libphy: 400d0000.etherne:00 - Link is Up - 100/Half
  libphy: 400d0000.etherne:00 - Link is Up - 100/Full
  libphy: 400d0000.etherne:00 - Link is Up - 100/Half

Add the missing module clock for ENET0 and ENET1, and correct the clock
supplying in device tree to fix above issue.

Thanks to Alison Wang <b18965@freescale.com> for debugging the issue.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>