x86: apl: Tell of-platdata about a required header file

This enum is needed to generate build-time devices. Tell dtoc where to
find the header, to avoid compile errors in the generated code.
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>

arch/x86/cpu/apollolake/punit.c

@@ -93,4 +93,5 @@ U_BOOT_DRIVER(intel_apl_punit) = {
 	.id		= UCLASS_SYSCON,
 	.of_match	= apl_syscon_ids,
 	.probe		= apl_punit_probe,
+	DM_HEADER(<asm/cpu.h>)    /* for X86_SYSCON_PUNIT */
 };