lib: sbi: Only register available extensions

When an extension implements a probe function it means there's a
chance that the extension is not available. Use this function in the
register_extensions callback to determine if the extension should be
registered at all. Where the probe implementation is simple, just
open code the check.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

lib/sbi/sbi_ecall_cppc.c

@@ -59,6 +59,9 @@ struct sbi_ecall_extension ecall_cppc;
 
 static int sbi_ecall_cppc_register_extensions(void)
 {
+	if (!sbi_cppc_get_device())
+		return 0;
+
 	return sbi_ecall_register_extension(&ecall_cppc);
 }