ipc_service: open-amp: Fix libmetal shared memory registration

When using multiple instances of IPC static vring, each instance
should register its shared memory with a unique name.
Instead of a predefined default name, the name of the ipc instance
is reused for the metal device name.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>