configs: Disable LRU_GEN_ENABLED on 32-bit kernels

We seem to be getting increased OOM failures with MGLRU
enabled on 32-bit kernels.
Let's disable it by default
(it can still be manually enabled at runtime).

See: https://github.com/raspberrypi/linux/issues/5395


Signed-off-by: Dom Cobley <popcornmix@gmail.com>