OvmfPkg/PlatformInitLib: Move 'First' variable to PlatformInfoHob

The static variable 'First' in function PlatformIgvmScanE820 in Igvm.c
used for debugging is part of the .data section. Initially, the variable
holds the boolean value 0x01, which changes during code execution to
0x00. As this change happens before the PEIFV measurement, and the
variable is part of the measurement, the measured PEIFV, which is
extended into PCR0, differs from the unbooted PEIFV. This difference
prevents precomputation of the expected value for PCR0, needed for
remote attestation.

Fix this by moving the variable into the PlatformInfoHob.

Co-authored-by: Simon Ott <simon.ott@aisec.fraunhofer.de>
Signed-off-by: Jakov Zauzolkov <jakov.zauzolkov@aisec.fraunhofer.de>