Convert CONFIG_BOOT_RETRY_TIME et al to Kconfig

This converts the following to Kconfig:
   CONFIG_BOOT_RETRY_TIME
   CONFIG_BOOT_RETRY_MIN
   CONFIG_RESET_TO_RETRY

We also introduce CONFIG_BOOT_RETRY to gate these options, and clean up
the associated Makefile entry and C code for picking default values of
CONFIG_BOOT_RETRY_MIN.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/boot/Makefile b/boot/Makefile
index 2938c3f..75366c8 100644
--- a/boot/Makefile
+++ b/boot/Makefile
@@ -5,11 +5,7 @@
 
 ifndef CONFIG_SPL_BUILD
 
-# This option is not just y/n - it can have a numeric value
-ifdef CONFIG_BOOT_RETRY_TIME
-obj-y += bootretry.o
-endif
-
+obj-$(CONFIG_BOOT_RETRY) += bootretry.o
 obj-$(CONFIG_CMD_BOOTM) += bootm.o bootm_os.o
 obj-$(CONFIG_CMD_BOOTZ) += bootm.o bootm_os.o
 obj-$(CONFIG_CMD_BOOTI) += bootm.o bootm_os.o