libmetal: Update branch for 2021.1 release
libmetal: Update branch for 2021.1 release

Signed-off-by: Christian Kohn <cddab1f837c400ff9c3b002761e2cb74669ec6d1@xilinx.com>
Signed-off-by: Jaewon Lee <1b369288d13b7b5cc9a37dd614e864b90fd18321@xilinx.com>

OpenAMP/meta-openamp,OpenAMP/meta-openamp