src/drivers: 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: Ib3a1cf04482a8f19b159c31cfb16a7b492748d91
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20352
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/drivers/pc80/rtc/mc146818rtc.c

@@ -28,7 +28,7 @@
 #include <cbfs.h>
 
 /* There's no way around this include guard. option_table.h is autogenerated */
-#if CONFIG_USE_OPTION_TABLE
+#if IS_ENABLED(CONFIG_USE_OPTION_TABLE)
 #include "option_table.h"
 #else
 #define LB_CKS_RANGE_START	0

src/drivers/pc80/rtc/mc146818rtc_romcc.c

@@ -1,7 +1,7 @@
 #include <stdint.h>
 #include <pc80/mc146818rtc.h>
 #include <fallback.h>
-#if CONFIG_USE_OPTION_TABLE
+#if IS_ENABLED(CONFIG_USE_OPTION_TABLE)
 #include "option_table.h"
 #endif
 
@@ -19,7 +19,7 @@ static int cmos_error(void)
 
 static int cmos_chksum_valid(void)
 {
-#if CONFIG_USE_OPTION_TABLE
+#if IS_ENABLED(CONFIG_USE_OPTION_TABLE)
 	unsigned char addr;
 	u16 sum, old_sum;
 
@@ -93,7 +93,7 @@ static inline __attribute__((unused)) int do_normal_boot(void)
 
 unsigned read_option_lowlevel(unsigned start, unsigned size, unsigned def)
 {
-#if CONFIG_USE_OPTION_TABLE
+#if IS_ENABLED(CONFIG_USE_OPTION_TABLE)
 	unsigned byte;
 
 	byte = cmos_read(start/8);