For sake of amthif consolidation move amthif specific code from
mei_write to mei_amthif_write

The original mei_amthif_write to mei_amthif_send_cmd
as this function deals with sending single command
while mei_amthif_write is interface function called from
the main driver which in turns calls mei_amthif_send_cmd
Signed-off-by: NTomas Winkler <tomas.winkler@intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Move AMT Host Interface functions into the new amthif.c file.
All functions has now common prefix: mei_amthif_
Signed-off-by: NTomas Winkler <tomas.winkler@intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>