cpu/intel: add IS_ENABLED() around Kconfig symbol references

Some of these can be changed from #if to if(), but that will happen
in a follow-on commmit.

Change-Id: Ie685bbbb1cbf06d32631ea40ad120b6f45374b2e
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20336
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/cpu/intel/turbo/turbo.c

@@ -19,7 +19,7 @@
 #include <cpu/x86/msr.h>
 #include <arch/cpu.h>
 
-#if CONFIG_CPU_INTEL_TURBO_NOT_PACKAGE_SCOPED
+#if IS_ENABLED(CONFIG_CPU_INTEL_TURBO_NOT_PACKAGE_SCOPED)
 static inline int get_global_turbo_state(void)
 {
 	return TURBO_UNKNOWN;