cyclic: use a flag in gd->flags for recursion protection

As a preparation for future patches, use a flag in gd->flags rather
than a separate member in (the singleton) struct cyclic_drv to keep
track of whether we're already inside cyclic_run().

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Stefan Roese <sr@denx.de>
Tested-by: Stefan Roese <sr@denx.de>
Tested-by: Tim Harvey <tharvey@gateworks.com> # imx8mm-venice-*

include/asm-generic/global_data.h

@@ -650,6 +650,10 @@ enum gd_flags {
 	 * @GD_FLG_FDT_CHANGED: Device tree change has been detected by tests
 	 */
 	GD_FLG_FDT_CHANGED = 0x100000,
+	/**
+	 * GD_FLG_CYCLIC_RUNNING: cyclic_run is in progress
+	 */
+	GD_FLG_CYCLIC_RUNNING = 0x200000,
 };
 
 #endif /* __ASSEMBLY__ */