mei: wait for hbm start non-interruptible

We cannot handle user interrupt in context of hbm start
so we only wait for time out which is reasonably short.

1. Add kdoc
2. Rename state to better reflect its function
3. Simplify wait condition and rename
   wait_recvd_msg to wait_hbm_start

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