x86: Move DSDT table to a writer function

Move this table over to use a writer function, moving the code from the
x86 implementation.

Add a pointer to the DSDT in struct acpi_ctx so we can reference it later.

Disable this table for sandbox since we don't actually compile real ASL
code.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/acpi/base.c b/lib/acpi/base.c
index 3e8d703..2057bd2 100644
--- a/lib/acpi/base.c
+++ b/lib/acpi/base.c
@@ -5,6 +5,8 @@
  * Copyright 2021 Google LLC
  */
 
+#define LOG_CATEGORY LOGC_ACPI
+
 #include <common.h>
 #include <acpi/acpi_table.h>
 #include <dm/acpi.h>