imx: mx6ul Add CONFIG_SYS_CACHELINE_SIZE for i.MX6UL

Since i.MX6UL's cache line size is 64bytes, need to
define the macro CONFIG_SYS_CACHELINE_SIZE to 64 for i.MX6UL.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>