x86: Move base tables to a writer function

Use the new ACPI writer to write the base tables at the start of the area,
moving this code from the x86 implementation.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/acpi/Makefile b/lib/acpi/Makefile
index 1318e83..4674a92 100644
--- a/lib/acpi/Makefile
+++ b/lib/acpi/Makefile
@@ -6,3 +6,8 @@
 obj-$(CONFIG_$(SPL_)ACPIGEN) += acpi_dp.o
 obj-$(CONFIG_$(SPL_)ACPIGEN) += acpi_table.o
 obj-y += acpi_writer.o
+
+# With QEMU the ACPI tables come from there, not from U-Boot
+ifndef CONFIG_QEMU
+obj-y += base.o
+endif