Kconfig: Migrate CONFIG_BOOTM_* options

Migrate all of the existing OS support options that are under
CONFIG_BOOTM_* to Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/mx7dsabresd_defconfig b/configs/mx7dsabresd_defconfig
index 1107507..b412358 100644
--- a/configs/mx7dsabresd_defconfig
+++ b/configs/mx7dsabresd_defconfig
@@ -14,6 +14,9 @@
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_BOOTD is not set
 CONFIG_CMD_BOOTZ=y
+# CONFIG_BOOTM_NETBSD is not set
+# CONFIG_BOOTM_PLAN9 is not set
+# CONFIG_BOOTM_RTEMS is not set
 # CONFIG_CMD_IMI is not set
 # CONFIG_CMD_XIMG is not set
 # CONFIG_CMD_EXPORTENV is not set