drivers/pc80/mc146818rtc: Reduce superfluous preprocessor use

cmos_init() had layers of preprocessor directives, which resulted in
a complete mess. Refactor it to make use of the IS_ENABLED() macro.
This improves readability significantly.

One of the changes is to remove in inline stub declaration of
(get|set)_option. Although that provided the ability for the compiler
to optimize out code when USE_OPTION_TABLE is not selected, there is
no evidence that such savings are measureable.

Change-Id: I07f00084d809adbb55031b2079f71136ade3028e
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/8306
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/include/pc80/mc146818rtc.h

@@ -169,21 +169,13 @@ static inline void cmos_write32(u8 offset, u32 value)
 #endif
 
 #if !defined(__ROMCC__)
-void cmos_init(int invalid);
+void cmos_init(bool invalid);
 void cmos_check_update_date(void);
-#if CONFIG_USE_OPTION_TABLE
+
 enum cb_err set_option(const char *name, void *val);
 enum cb_err get_option(void *dest, const char *name);
 unsigned read_option_lowlevel(unsigned start, unsigned size, unsigned def);
-#else
-static inline enum cb_err set_option(const char *name __attribute__((unused)),
-				     void *val __attribute__((unused)))
-				{ return CB_CMOS_OTABLE_DISABLED; };
-static inline enum cb_err get_option(void *dest __attribute__((unused)),
-				     const char *name __attribute__((unused)))
-				{ return CB_CMOS_OTABLE_DISABLED; }
-#define read_option_lowlevel(start, size, def) def
-#endif
+
 #else /* defined(__ROMCC__) */
 #include <drivers/pc80/mc146818rtc_early.c>
 #endif /* !defined(__ROMCC__) */