x86: Record the start and end of the tables

The ACPI tables are special in that they are passed to EFI as a separate
piece, independent of other tables.

Also they can be spread over two areas of memory, e.g. with QEMU we end
up with tables kept in high memory as well.

Add new global_data fields to hold this information and update the bdinfo
command to show the table areas.

Move the rom_table_end variable into the loop that uses it.

Change-Id: Ide1869a9d0ecb96f573e5a1a8667450437a3143e
Signed-off-by: Simon Glass <sjg@chromium.org>