mei: me: add a wrapper to set host generated data interrupt

Consolidate setting H_IG, an interrupt from host towards hw,
into a wrapper to eliminate code duplication.

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>