bootcount: flush after storing the bootcounter

If the bootcounter address is in a cached memory,
a flush of dcache must occur after updateing the bootcounter.

Issue found on i.MX6 where bootcounter is put into the internal
(cached) IRAM.

Signed-off-by: Stefano Babic <sbabic@denx.de>

drivers/bootcount/bootcount.c

@@ -18,6 +18,9 @@ __weak void bootcount_store(ulong a)
 	raw_bootcount_store(reg, a);
 	raw_bootcount_store(reg + 4, BOOTCOUNT_MAGIC);
 #endif /* defined(CONFIG_SYS_BOOTCOUNT_SINGLEWORD */
+	flush_dcache_range(CONFIG_SYS_BOOTCOUNT_ADDR,
+				CONFIG_SYS_BOOTCOUNT_ADDR +
+				CONFIG_SYS_CACHELINE_SIZE);
 }
 
 __weak ulong bootcount_load(void)