-moutline-atomics allows LSE instructions to be used if available when
compiling for ARMv8.0 instruction set. It's enabled by default on newer
compilers, such as gcc-10.1. Enable the option in case an earlier
compiler version is used for the default build that lacks either -mcpu
or -mtune which would otherwise enable it.
Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>