net: airoha: Wait for NPU PPE configuration to complete in airoha_ppe_offload_setup()

net: airoha: Wait for NPU PPE configuration to complete in airoha_ppe_offload_setup()

In order to properly enable flowtable hw offloading, poll
REG_PPE_FLOW_CFG register in airoha_ppe_offload_setup routine and
wait for NPU PPE configuration triggered by ppe_init callback to complete
before running airoha_ppe_hw_init().

Fixes: 00a7678310fe3 ("net: airoha: Introduce flowtable offload support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260414-airoha-wait-for-npu-config-offload-setup-v2-1-5a9bf6d43aee@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>