imx: hab: Check if CSF is valid before authenticating image

imx: hab: Check if CSF is valid before authenticating image

For proper authentication the HAB code must check if the CSF is valid.
Users must call the csf_is_valid() function to parse the CSF prior to
authenticating any additional images. The function will return a failure
if any of the following invalid conditions are met:

- CSF pointer is NULL
- CSF Header does not exist
- CSF does not lie within the image bounds
- CSF command length zero

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