Convert CONFIG_SYS_BOOTCOUNT_LE et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_BOOTCOUNT_LE
   CONFIG_SYS_BOOTCOUNT_BE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/bootcount/Kconfig b/drivers/bootcount/Kconfig
index 66ce4cc..e918f74 100644
--- a/drivers/bootcount/Kconfig
+++ b/drivers/bootcount/Kconfig
@@ -237,4 +237,15 @@
 	help
 	  Set the magic value used for the boot counter.
 
+choice
+	prompt "Endianness of bootcount accessors"
+	default SYS_BOOTCOUNT_LE
+
+config SYS_BOOTCOUNT_LE
+	bool "Little endian accessors"
+
+config SYS_BOOTCOUNT_BE
+	bool "Big endian accessors"
+
+endchoice
 endif