OvmfPkg/GenericQemuLoadImageLib: log "Not Found" at INFO level

gBS->LoadImage() returning EFI_NOT_FOUND is an expected condition; it
means that QEMU wasn't started with "-kernel". Log this status code as
INFO rather than ERROR.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200609105414.12474-1-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>