i.MX6UL features an Cortex-A7 core, it does not have PL310 as other i.MX6
chips. To Cortex-A7 core, If D-Cache is enabled, L2 Cache is enabled.
There is on specific switch for on/off L2 Cache, so default select
SYS_L2CACHE_OFF.
Signed-off-by: NPeng Fan <Peng.Fan@freescale.com>