riscv: Add board_quiesce_devices stub

This patch adds an empty stub for board_quiesce_devices() which allows boards
to quiesce their devices before we boot into an OS in a platform agnostic way.

Signed-off-by: Alexander Graf <agraf@suse.de>

arch/riscv/include/asm/u-boot-riscv.h

@@ -16,5 +16,6 @@ int cleanup_before_linux(void);
 
 /* board/.../... */
 int board_init(void);
+void board_quiesce_devices(void);
 
 #endif	/* _U_BOOT_RISCV_H_ */

arch/riscv/lib/bootm.c

@@ -15,6 +15,10 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
+__weak void board_quiesce_devices(void)
+{
+}
+
 int arch_fixup_fdt(void *blob)
 {
 	return 0;