powerpc/mpc83xx: set TXEQA/TXEQE value for mpc837XE sata

powerpc/mpc83xx: set TXEQA/TXEQE value for mpc837XE sata

In the current u-boot code, the value of these fields are the reserved
value (0b100), through the signal integrity measurement on freescale's
board with these reserved setting, the signal eye is out of the recommended
spec for non-transition amplitude at 500mV nominal.
According to the errata for MPC8379E, we should make a change to the
recommended setting from essentially nothing at this time to 0b001 for SATA.

Signed-off-by: Jerry Huang <Chang-Ming.Huang@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>