bootcount: Make bootcount magic configurable

Add new Kconfig option, SYS_BOOTCOUNT_MAGIC, to select the boot
counter magic word. This can be useful ie. in case the entire
boot counter register is not usable.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@konsulko.com>
diff --git a/drivers/bootcount/bootcount.c b/drivers/bootcount/bootcount.c
index 646c563..66c1284 100644
--- a/drivers/bootcount/bootcount.c
+++ b/drivers/bootcount/bootcount.c
@@ -16,13 +16,13 @@
 	uintptr_t flush_end;
 
 #if defined(CONFIG_SYS_BOOTCOUNT_SINGLEWORD)
-	raw_bootcount_store(reg, (BOOTCOUNT_MAGIC & 0xffff0000) | a);
+	raw_bootcount_store(reg, (CONFIG_SYS_BOOTCOUNT_MAGIC & 0xffff0000) | a);
 
 	flush_end = roundup(CONFIG_SYS_BOOTCOUNT_ADDR + 4,
 			    CONFIG_SYS_CACHELINE_SIZE);
 #else
 	raw_bootcount_store(reg, a);
-	raw_bootcount_store(reg + 4, BOOTCOUNT_MAGIC);
+	raw_bootcount_store(reg + 4, CONFIG_SYS_BOOTCOUNT_MAGIC);
 
 	flush_end = roundup(CONFIG_SYS_BOOTCOUNT_ADDR + 8,
 			    CONFIG_SYS_CACHELINE_SIZE);
@@ -37,12 +37,12 @@
 #if defined(CONFIG_SYS_BOOTCOUNT_SINGLEWORD)
 	u32 tmp = raw_bootcount_load(reg);
 
-	if ((tmp & 0xffff0000) != (BOOTCOUNT_MAGIC & 0xffff0000))
+	if ((tmp & 0xffff0000) != (CONFIG_SYS_BOOTCOUNT_MAGIC & 0xffff0000))
 		return 0;
 	else
 		return (tmp & 0x0000ffff);
 #else
-	if (raw_bootcount_load(reg + 4) != BOOTCOUNT_MAGIC)
+	if (raw_bootcount_load(reg + 4) != CONFIG_SYS_BOOTCOUNT_MAGIC)
 		return 0;
 	else
 		return raw_bootcount_load(reg);