cmd/sbi: add implementation ID 6 - Coffer

The sbi command displays the ID of the implementation of the RISC-V
Supervisor Binary Interface Specification. A new ID for Coffer has recently
been added.
Signed-off-by: NHeinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: NLeo Yu-Chi Liang <ycliang@andestech.com>

cmd/riscv/sbi.c

@@ -26,6 +26,7 @@ static struct sbi_imp implementations[] = {
 	{ 3, "KVM" },
 	{ 4, "RustSBI" },
 	{ 5, "Diosix" },
+	{ 6, "Coffer" },
 };
 
 static struct sbi_ext extensions[] = {