Running/building an 32 bits kernel on A53 CPU?

[Joakim Tjernlund]

In order to reduce RAM usage we are wondering if running an 32 bits kernel on ARM A53 CPU is a good idea?

Is it possible to build such a kernel? If so, how to go about it?
Should one use ARCH=arm and a 32 bits toolchain or
ARCH=arm64 and 64 bits toolchain and adding 32 bits compile options?

 Jocke