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/imx8qm_mek_defconfig b/configs/imx8qm_mek_defconfig
index 3294931..42591c7 100644
--- a/configs/imx8qm_mek_defconfig
+++ b/configs/imx8qm_mek_defconfig
@@ -24,6 +24,7 @@
 CONFIG_SPL_POWER_DOMAIN=y
 CONFIG_SPL_WATCHDOG_SUPPORT=y
 CONFIG_CMD_CPU=y
+# CONFIG_BOOTM_NETBSD is not set
 # CONFIG_CMD_IMPORTENV is not set
 CONFIG_CMD_CLK=y
 CONFIG_CMD_DM=y