doc: mxc_hab: Improve the config option list

The original text is from the time that the config options were not
converted to Kconfig.

After the conversion to Kconfig only CONFIG_SECURE_BOOT and
CONFIG_CMD_DEKBLOB need to be selected by the user.

The other config options are automatically selected by the Kconfig
logic.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Breno Lima <breno.lima@nxp.com>