acpi: add helper routines to initialize ACPI tables

acpi: add helper routines to initialize ACPI tables

Patch introduces acpi_table_begin()/ acpi_table_end() API
that hides pointer/offset arithmetic from user as opposed
to build_header(), to prevent errors caused by it [1].

 acpi_table_begin():
     initializes table header and keeps track of
     table data/offsets
 acpi_table_end():
     sets actual table length and tells bios loader
     where table is for the later initialization on
     guest side.

1) commits
   bb9feea43179 x86: acpi: use offset instead of pointer when using build_header()
   4d027afeb3a9 Virt: ACPI: fix qemu assert due to re-assigned table data address

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20210924122802.1455362-2-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Yanan Wang <wangyanan55@huawei.com>