Modified the DDR SDRAM clock control register to delay MCK/MCK_B 3/4 clock

Modified the DDR SDRAM clock control register to delay MCK/MCK_B 3/4 clock

With the original value of 1/2 clock cycle delay, the system ran relatively
stable except when we run benchmarks that are intensive users of memory.
When I run samba connected disk with a HDBENCH test, the system locks-up
or reboots sporadically.

Signed-off by: Joe D'Abbraccio <Joe.D'abbraccio@freescale.com>