bootcounter: add DM support for memory based bootcounter

add DM/DTS support for the memory based bootcounter
in drivers/bootcount/bootcount.c.

Let the old implementation in, so boards which have
not yet convert to DM/DTS do not break.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/bootcount/Kconfig b/drivers/bootcount/Kconfig
index 0e506c9..0356f8b 100644
--- a/drivers/bootcount/Kconfig
+++ b/drivers/bootcount/Kconfig
@@ -106,6 +106,13 @@
 	  pointing to the underlying i2c eeprom device) and an optional 'offset'
 	  property are supported.
 
+config BOOTCOUNT_MEM
+	bool "Support memory based bootcounter"
+	help
+	  Enabling Memory based bootcount, typically in a SoC register which
+	  is not cleared on softreset.
+	  compatible = "u-boot,bootcount";
+
 endmenu
 
 endif