fwu: meta-data: switch to management by common code

The common code can now read, verify and fix meta-data copies
while exposing one consistent structure to users.
 Only the .read_mdata() and .write_mdata() callbacks of fwu_mdata_ops
are needed. Get rid of .get_mdata() .update_mdata() .get_mdata_part_num()
.read_mdata_partition() and .write_mdata_partition() and also the
corresponding wrapper functions.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Tested-by: Sughosh Ganu <sughosh.ganu@linaro.org>