acpi: take oem_id in build_header(), optionally

This patch is the continuation of commit 8870ca0e ("acpi: support
specified oem table id for build_header"). It will allow us to control the
OEM ID field too in the SDT header.

Cc: "Michael S. Tsirkin" <mst@redhat.com> (supporter:ACPI/SMBIOS)
Cc: Igor Mammedov <imammedo@redhat.com> (supporter:ACPI/SMBIOS)
Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com> (maintainer:NVDIMM)
Cc: Shannon Zhao <zhaoshenglong@huawei.com> (maintainer:ARM ACPI Subsystem)
Cc: Paolo Bonzini <pbonzini@redhat.com> (maintainer:X86)
Cc: Richard W.M. Jones <rjones@redhat.com>
Cc: Aleksei Kovura <alex3kov@zoho.com>
Cc: Michael Tokarev <mjt@tls.msk.ru>
Cc: Steven Newbury <steve@snewbury.org.uk>
RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1248758
LP: https://bugs.launchpad.net/qemu/+bug/1533848


Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Shannon Zhao <shannon.zhao@linaro.org>