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

Change-Id: I2b532522938123bb7844cef94cda0b44bcb98e45
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20350
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/southbridge/intel/ibexpeak/pch.h

@@ -70,7 +70,7 @@ int pch_silicon_type(void);
 int pch_silicon_supported(int type, int rev);
 void pch_iobp_update(u32 address, u32 andvalue, u32 orvalue);
 void gpi_route_interrupt(u8 gpi, u8 mode);
-#if CONFIG_ELOG
+#if IS_ENABLED(CONFIG_ELOG)
 void pch_log_state(void);
 #endif
 #else /* __PRE_RAM__ */