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/configs/rastaban_defconfig b/configs/rastaban_defconfig
index 9820088..240304e 100644
--- a/configs/rastaban_defconfig
+++ b/configs/rastaban_defconfig
@@ -28,6 +28,9 @@
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="Autobooting in %d seconds, press \"<Esc><Esc>\" to stop\n"
 CONFIG_AUTOBOOT_STOP_STR="\x1b\x1b"
+CONFIG_BOOT_RETRY=y
+CONFIG_BOOT_RETRY_TIME=60
+CONFIG_RESET_TO_RETRY=y
 CONFIG_USE_PREBOOT=y
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 # CONFIG_DISPLAY_BOARDINFO is not set