feat(plat/imx/imx8m/imx8mm): add support for measured boot

Add helper functions to generate event log for imx8mm
when MEASURED_BOOT=1.

Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
Change-Id: Ifc947d749055787fbda0b39170aa2eb8865b7802