cpu/x86: Introduce CPU_X86_CACHE_HELPER

There's no need for relative paths with Kconfig options.

Change-Id: Ib9b9b29a158c34a30480aaabf6d0b23819d28427
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44226
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

src/cpu/x86/Kconfig

@@ -1,3 +1,9 @@
+config CPU_X86_CACHE_HELPER
+	bool
+	default n
+	help
+	  Add the x86_enable_cache ramstage helper function to the build.
+
 config PARALLEL_MP
 	def_bool y
 	depends on !LEGACY_SMP_INIT

src/cpu/x86/Makefile.inc

@@ -1,3 +1,4 @@
+subdirs-$(CONFIG_CPU_X86_CACHE_HELPER) += cache
 subdirs-y += mtrr
 subdirs-y += pae
 subdirs-$(CONFIG_HAVE_SMI_HANDLER) += smm