lib: Factor-out SBI legacy extension

This patch factor-out SBI legacy extension into its own source
for better modularity of SBI implementation.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

include/sbi/sbi_ecall.h

@@ -29,6 +29,8 @@ struct sbi_ecall_extension {
 		       struct sbi_trap_info *out_trap);
 };
 
+extern struct sbi_ecall_extension ecall_legacy;
+
 u16 sbi_ecall_version_major(void);
 
 u16 sbi_ecall_version_minor(void);