extres: regulator: fix the build without FDT

The regnode interface is currently only built for FDT, thus not
applicable to ACPI-only kernels.  Move the "regnode_if.h" include
underneath a previously existing FDT cpp segment.

Reviewed by:	andrew, imp, manu
Differential Revision:	https://reviews.freebsd.org/D36790

sys/dev/extres/regulator/regulator.h

@@ -34,8 +34,8 @@
 #include <sys/sysctl.h>
 #ifdef FDT
 #include <dev/ofw/ofw_bus.h>
-#endif
 #include "regnode_if.h"
+#endif
 
 SYSCTL_DECL(_hw_regulator);