cmd: sbi: add Performance Monitoring Unit Extension

Version 1.0-rc3 of the RISC-V Supervisor Binary Interface Specification
has added the Performance Monitoring Unit Extension.

The sbi command should be able to detect it.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/cmd/riscv/sbi.c b/cmd/riscv/sbi.c
index c4a9c84..8349123 100644
--- a/cmd/riscv/sbi.c
+++ b/cmd/riscv/sbi.c
@@ -44,6 +44,7 @@
 	{ SBI_EXT_RFENCE,		      "RFENCE Extension" },
 	{ SBI_EXT_HSM,			      "Hart State Management Extension" },
 	{ SBI_EXT_SRST,			      "System Reset Extension" },
+	{ SBI_EXT_PMU,			      "Performance Monitoring Unit Extension" },
 };
 
 static int do_sbi(struct cmd_tbl *cmdtp, int flag, int argc,