Signing on i.MX8MQ is done by signing only the PBL, since the DRAM is
not available on early start and the SRAM is not big enough to contain
the whole image. Reserve a CSF area between PBL and the piggydata, to
ensure that the CSF area can be loaded into SRAM.

Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>