powerpc/t1040qds: Update DDR initialization related settings

Update following DDR related settings for T1040QDS
-Correct number of chip selects to two as t1040qds supports
 two Chip selects.
-Update board_specific_parameters udimm structure with settings
 derived via calibration.
-Reduced I2C speed to 50KHz as DDR-SPD does not get reliably
 read at 400KHz.

Verified the updated settings to be working fine with dual-ranked
Micron, MT18KSF51272AZ-1G6 DIMM at data rate 833MT/s, 1333MT/s and
1600MT/s.

Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>