net: airoha: Introduce airoha_qdma struct

Introduce airoha_qdma struct and move qdma IO register mapping in
airoha_qdma. This is a preliminary patch to enable both QDMA controllers
available on EN7581 SoC.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/7df163bdc72ee29c3d27a0cbf54522ffeeafe53c.1722522582.git.lorenzo@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>