configs: lx2160a: Add default config for lx2160a using StMM in OP-TEE

Previous patches allow UEFI secure variables to be stored in an RPMB
device using OPTEE. Add a config for the lx2160a hardware so the feature
gets at least compiled.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Remove superfluous differences to lx2160ardb_tfa_defconfig.
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>