util/cbfstool: Defuse vboot's openssl linking

Vboot determines openssl through pkgconfig, so pointing its build
system to /bin/true makes the build not break unless it needs to use
valid information about openssl.

Vboot's use of openssl is only for some special features, mostly around
PKCS key format parsing and not needed by cbfstool. While cbfstool
can link vboot, it can't link with openssl because openssl's license
is deliberately incompatible with the GPL.

Change-Id: Ia3825f9625a1964d7cefc47ab3c3a8250ceefafb
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42880
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

util/cbfstool/Makefile.inc

@@ -133,7 +133,7 @@ $(VBOOT_HOSTLIB):
 	unset CFLAGS LDFLAGS; $(MAKE) -C $(VBOOT_SOURCE) \
 		BUILD=$(VBOOT_HOST_BUILD) \
 		CC="$(HOSTCC)" \
-		$(if $(HOSTPKGCONFIG), PKG_CONFIG="$(HOSTPKGCONFIG)") \
+		PKG_CONFIG="true" \
 		V=$(V) \
 		hostlib