Makefile: Make pkg-config mandatory to find libftdi1

Use `make HAS_LIBFTDI1=yes/no` to override the pkg-config detection and
`CONFIG_LIBFTDI1_CFLAGS` and `CONFIG_LIBFTDI1_LDFLAGS` to set cflags and
ldflags manually.

Change-Id: I41f5186d9f3e063c12c8c6eea888d0b0bf534259
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/58623
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

Makefile.d/ft232h_test.c

@@ -0,0 +1,3 @@
+#include <ftdi.h>
+
+enum ftdi_chip_type type = TYPE_232H;