wil6210: add NIC memory region mac_rgf_ext

Firmware defines new memory region, mac_rgf_ext
that need to be accessed from the host for debug purposes.

Add corresponded mapping

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>