lib/fmap: Disable pre-RAM cache for FSP 1.0

Due to the way CAR teardown is handled in FSP 1.0, the results of
car_get_var_ptr() aren't always reliable, which can break things when
running with FMAP cache. It might be possible to fix this but would make
the code rather complicated, so let's just disable the feature on these
platforms and hope they die out soon.

Also allow this option to be used by platforms that don't have space for
the cache and want to save a little more code.

Change-Id: I7ffb1b8b08a7ca3fe8d53dc827e2c8521da064c7
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36937
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/lib/Kconfig

@@ -68,3 +68,10 @@ config HWBASE_DIRECT_PCIDEV
 	def_bool y
 
 endif
+
+config NO_FMAP_CACHE
+	bool
+	help
+	  If your platform really doesn't want to use an FMAP cache (e.g. due to
+	  space constraints), you can select this to disable warnings and save
+	  a bit more code.