mei: bus: move driver api functions at the start of the file

[ Upstream commit 62382997 ]

To make the file more organize move mei client driver api
to the start of the file and add Kdoc.

There are no functional changes in this patch.

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