cmd/riscv/sbi: support System Reset Extension

Let the sbi command detect the 'System Reset Extension'
(EID #0x53525354 "SRST").

Cf. https://github.com/riscv/riscv-sbi-doc

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Pragnesh Patel <pragnesh.patel@openfive.com>
Reviewed-by: Leo Liang <ycliang@andestech.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>

cmd/riscv/sbi.c

@@ -43,6 +43,7 @@ static struct sbi_ext extensions[] = {
 	{ 0x00735049, "IPI Extension" },
 	{ 0x52464E43, "RFENCE Extension" },
 	{ 0x0048534D, "Hart State Management Extension" },
+	{ 0x53525354, "System Reset Extension" },
 };
 
 static int do_sbi(struct cmd_tbl *cmdtp, int flag, int argc,