libmetal: include libmetal demo to libmetal recipe
libmetal: include libmetal demo to libmetal recipe

Also build libmetal demos in the libmetal recipe

Signed-off-by: Wendy Liang <cac46fad14f88489ab4dbc3c1082c7dafae20187@xilinx.com>

OpenAMP/meta-openamp,OpenAMP/meta-openamp