Migrate generic bootcount to Kconfig

Make generate boot counter selected in the same way as other boot count
drivers

Reviewed-by: Lukasz Majewski <lukma@denx.de>
Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
diff --git a/drivers/bootcount/Makefile b/drivers/bootcount/Makefile
index a3658c1..3e1ae8c 100644
--- a/drivers/bootcount/Makefile
+++ b/drivers/bootcount/Makefile
@@ -2,7 +2,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-y				+= bootcount.o
+obj-$(CONFIG_BOOTCOUNT_GENERIC)	+= bootcount.o
 obj-$(CONFIG_BOOTCOUNT_AT91)	+= bootcount_at91.o
 obj-$(CONFIG_BOOTCOUNT_AM33XX)	+= bootcount_davinci.o
 obj-$(CONFIG_BOOTCOUNT_RAM)	+= bootcount_ram.o