This commit lets the nRF port use the new
MICROPY_PERSISTENT_CODE_LOAD_NATIVE configuration entry.
The nRF port needs a special procedure to allocate memory used to hold
executable native code. This functionality was gated behind the
presence of a native emitter and thus its inclusion condition had to be
updated.
Signed-off-by: Alessandro Gatti <a.gatti@frob.it>