x86: Move CSRT table to a writer function

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

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/acpi/Makefile b/lib/acpi/Makefile
index 552d499..f9b5049 100644
--- a/lib/acpi/Makefile
+++ b/lib/acpi/Makefile
@@ -10,6 +10,7 @@
 # With QEMU the ACPI tables come from there, not from U-Boot
 ifndef CONFIG_QEMU
 obj-y += base.o
+obj-y += csrt.o
 
 # Sandbox does not build a .asl file
 ifndef CONFIG_SANDBOX