plat: imx8mm: Add imx8mm_private.h to the build

Allows for exporting of FIP related methods cleanly in a private header.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
Change-Id: I8523f1370312ed22ff7ca710cd916be52f725e3c
1 file changed