docker/coreboot-sdk: Replace 'pkg-config' with 'pkgconf'

Replace transitional 'pkg-config' package with 'pkgconf'.

Change-Id: I9ee895cb2ca3186c4aefbdab1fd71778bf981009
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82167
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/docker/coreboot-sdk/Dockerfile

@@ -72,7 +72,7 @@ RUN \
 		parted \
 		patch \
 		pbzip2 \
-		pkg-config \
+		pkgconf \
 		python3 \
 		python-is-python3 \
 		qemu-system-arm \