wifi(implementation): Load wifi driver on IWifi.start()

The current implementation loads the wifi driver only when the chip is
configured, but the HAL is initialized on IWifi.start(). This seems to
be wrong semantically. The driver needs to be loaded before the HAL is
initialized.

This may have worked previously because the driver was loaded in
init.rc, but may stop working when we move to proper DLKM model in 2018.

Bug: 65671875
Test: Device boots up and connects to wifi networks.
Change-Id: I017d3528bf0b42a6a59af43203ecc9d0d027f60d