src: add IS_ENABLED() around Kconfig symbol references

These are places that were missed on the first pass.

Change-Id: Ia6511f0325433ab020946078923bf7ad6f0362a3
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20358
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/console/vtxprintf.c

@@ -21,7 +21,7 @@
 
 #define call_tx(x) tx_byte(x, data)
 
-#if !CONFIG_ARCH_MIPS
+#if !IS_ENABLED(CONFIG_ARCH_MIPS)
 #define SUPPORT_64BIT_INTS
 #endif