net: airoha: npu: Move memory allocation in airoha_npu_send_msg() caller

Move ppe_mbox_data struct memory allocation from airoha_npu_send_msg
routine to the caller one. This is a preliminary patch to enable wlan NPU
offloading and flow counter stats support.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250516-airoha-en7581-flowstats-v2-1-06d5fbf28984@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>