boot: Make missing CHID DTB match a debug message instead of an error

boot: Make missing CHID DTB match a debug message instead of an error

With distributions like Ubuntu and Fedora using systemd-stub to auto load
DTB's on Windows on ARM laptops, the CHID DTB match failing is expected
when that same UKI is instead booted on an ARM SystemReady system where
no DTB is necessary.

In the ARM SystemReady case showing a big red error message is undesirable
and leads to confused users and bug-reports. Lower the message to debug
level when the status is EFI_NOT_FOUND to avoid these false positive error
messages.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2444759