guid-tool.yaml: add i.MX8M Plus EVK GUID

The NXP i.MX8M Plus EVK is certified for SystemReady IR 2.0 (with SIE);
keep track of its GUID accordingly.

[Backport commit 6e7cc0c9 ("guid-tool.yaml: add i.MX8M Plus EVK
GUID").]
Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>