hotspot: change HAL integration to MechanicD
We no longer patch wpa_supplicant just to add single custom method. Alfred's MechanicD is already included for Aethercast. We have to switch to that to use Wi-Fi HAL for STA/AP mode switching. With that, we'll also be able to get rid of MTK-specific method, as Wi-Fi HAL should cover that as well.