Verify Kconfigs symbols are not zero for hex and int type symbols

For hex and int type kconfig symbols, IS_ENABLED() doesn't work. Instead
check to make sure they're defined and not zero.  In some cases, zero
might be a valid value, but it didn't look like zero was valid in these
cases.

Change-Id: Ib51fb31b3babffbf25ed3ae4ed11a2dc9a4be709
Signed-off-by: Martin Roth <gaumless@gmail.com>
Reviewed-on: http://review.coreboot.org/10886
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/cpu/x86/mtrr/earlymtrr.c

@@ -50,7 +50,7 @@ static void do_early_mtrr_init(const unsigned long *mtrr_msrs)
 		wrmsr(msr_nr, msr);
 	}
 
-#if defined(CONFIG_XIP_ROM_SIZE)
+#if defined(CONFIG_XIP_ROM_SIZE) && CONFIG_XIP_ROM_SIZE
 	/* enable write through caching so we can do execute in place
 	 * on the flash rom.
 	 * Determine address by calculating the XIP_ROM_SIZE sized area with