refactor(plat/imx/imx8m): make image load logic for TBBR FIP booting common

This commit makes the image load logic from imx8mm common for all
imx8m platform.

Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
Change-Id: Ibfe2e9cc09d198cb9e309afaf381a0237a4b82ed
2 files changed