x86: acpi: Store the ACPI context in global_data

At present we create the ACPI context but then drop it after generation of
tables is complete. This is annoying because we have to then search for
tables later.

To fix this, allocate the context and store it in global_data.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/lib/acpi_table.c b/arch/x86/lib/acpi_table.c
index 6d405b0..f0f342d 100644
--- a/arch/x86/lib/acpi_table.c
+++ b/arch/x86/lib/acpi_table.c
@@ -494,7 +494,7 @@
  */
 ulong write_acpi_tables(ulong start_addr)
 {
-	struct acpi_ctx sctx, *ctx = &sctx;
+	struct acpi_ctx *ctx;
 	struct acpi_facs *facs;
 	struct acpi_table_header *dsdt;
 	struct acpi_fadt *fadt;
@@ -509,6 +509,11 @@
 	int ret;
 	int i;
 
+	ctx = calloc(1, sizeof(*ctx));
+	if (!ctx)
+		return log_msg_ret("mem", -ENOMEM);
+	gd->acpi_ctx = ctx;
+
 	start = map_sysmem(start_addr, 0);
 
 	debug("ACPI: Writing ACPI tables at %lx\n", start_addr);