soletta-basic: make it build for samr21-xpro
soletta-basic: make it build for samr21-xpro

Signed-off-by: Bruno Dilly <ea4fb6320c1221b6a559089d8ab97ffc53fc6586@intel.com>

solettaproject/soletta-small-oses-samples,solettaproject/soletta-riot-samples