riscv: Avoid calling sbi_clear_ipi()

There is no need for S-mode U-Boot to call sbi_clear_ipi() as it
can be cleared directly from S-mode. This saves some cycles.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas@auer.io>
diff --git a/arch/riscv/lib/sbi_ipi.c b/arch/riscv/lib/sbi_ipi.c
index 9a698ce..abafca9 100644
--- a/arch/riscv/lib/sbi_ipi.c
+++ b/arch/riscv/lib/sbi_ipi.c
@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <asm/encoding.h>
 #include <asm/sbi.h>
 
 int riscv_send_ipi(int hart)
@@ -19,7 +20,7 @@
 
 int riscv_clear_ipi(int hart)
 {
-	sbi_clear_ipi();
+	csr_clear(CSR_SIP, SIP_SSIP);
 
 	return 0;
 }