feat(imx8mn): optionally take params from BL2

Optionally take params from BL2 to offer more flexibility to BL2 on
where and if a BL32 image is expected. This uses imx_bl31_params_parse()
to check if arg0 can safely be accessed as a pointer and actually
contains a bl_params_t structure. If not, the hardcoded parameter
values are used as before.

Change-Id: Ia12d35778f4d550860e517f2a1f5c5d062f3283a
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
3 files changed