verifyDTBO: update to use bootconfig

Update verifyDTBO.sh to match the VTS tests FirmwareDtboVerification
which first checks the bootconfig for the dtbo_idx. If it doesn't find
it, then check the kernel command line.

Bug: 265256786
Tested: run ./verifyDTBO.sh on an oriole
Change-Id: I50f6f6a22736f8b367bd140cd3e5e0e68dbe6cea
1 file changed