mei: simplify preparing client host bus messages

Define a new parent type mei_hbm_cl_cmd for hbm
commands that are sent on behalf of specific ME client.
This allows us compacting boilerplate code via mei_hbm_cl_hdr
function

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