bmips: enable the data Read Ahead Cache for BMIPS4350

bmips: enable the data Read Ahead Cache for BMIPS4350

The data RAC is left disabled by the bootloader in some SoCs, at least in
the core it boots from. Enabling this feature increases the performance up
to +30% depending on the task.

The kernel enables the whole RAC unconditionally on BMIPS3300 CPUs. Enable
the data RAC in a similar way also for BMIPS4350.

Tested on DGND3700 v1 (BCM6368) and HG556a (BCM6358).

Signed-off-by: Daniel González Cabanelas <dgcbueu@gmail.com>
(cherry picked from commit 6d1265b14850abaf8980e5cebef3e559b1fdcfb9)