powerpc/c29xpcie: Getting DDR SPD image from 16-bit sub-address EEPROM

Currently, there is only one EEPROM on c29xpcie board which is AT24C1024.
We program the SPD data at beginning of the AT24C1024.But the AT24C1024
has a 16-bit sub-address mode. This patch is tomake it work when getting
SPD in a 16-bit sub-address EEPROM.

Signed-off-by: Po Liu <Po.Liu@freescale.com>
Acked-by: York Sun <yorksun@freescale.com>