src/: Fix Kcofig symbols missing CONFIG_ prefix

- Add CONFIG_ prefix to two symbols.
- Remove the use of the third symbol as it will never be matched.

Change-Id: Ifa7f6884001cb05fb8397f193c4b08a0161f498c
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/13539
Tested-by: build bot (Jenkins)
Tested-by: Raptor Engineering Automated Test Stand <noreply@raptorengineeringinc.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/cpu/amd/car/disable_cache_as_ram.c

@@ -72,7 +72,7 @@ static inline __attribute__((always_inline)) void disable_cache_as_ram(uint8_t s
 
 	family = amd_fam1x_cpu_family();
 
-#if IS_ENABLED(CPU_AMD_MODEL_10XXX)
+#if IS_ENABLED(CONFIG_CPU_AMD_MODEL_10XXX)
 	if (family >= 0x6f) {
 		/* Family 15h or later */