configs/omnia: upstream changed name of Turris Omnia target

Upstream prefixed manufacturer name to target config. This is somewhat
nasty of them but we should stay consistent with them. This updates our
configuration to use that target instead.

configs/omnia/basic-hw

 CONFIG_TARGET_mvebu=y
 CONFIG_TARGET_mvebu_cortexa9=y
-CONFIG_TARGET_mvebu_cortexa9_DEVICE_turris-omnia=y
+CONFIG_TARGET_mvebu_cortexa9_DEVICE_cznic_turris-omnia=y
 CONFIG_HAS_SUBTARGETS=y
 CONFIG_HAS_DEVICES=y
 CONFIG_TARGET_BOARD="mvebu"