Makefile: Make pkg-config mandatory to find libpci

Use `make HAS_LIBPCI=yes/no` to override the pkg-config detection and
`CONFIG_LIBPCI_CFLAGS` and `CONFIG_LIBPCI_LDFLAGS` to set cflags and
ldflags manually. The optional dependency of libpci libz, is
automatically handled by pkg-config.

Change-Id: I21b4a261b34b7e688635fc6e20b7beebfa64c7ed
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/59050
Original-Reviewed-by: Nico Huber <nico.h@gmx.de>
Original-Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72281
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
3 files changed