uboot-imx

mx23: Document the tRAS lockout setting in memory initialization

Add a comment about the tRAS lockout setting of HW_DRAM_CTL08 to
enable the 'Fast Auto Pre-Charge' found in the memory chip. The
setting is applied after memory initialization and it is worth
document it.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>