mei: add hw start callback

This callback wraps up hardware dependent details
of the hardware initialization.

This callback also contains host ready setting
so we can remove host_set_ready callback

In ME we switch to waiting on event so
we can streamline the initialization flow.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>