util/docker/coreboot-sdk: add graphicsmagick-imagemagick-compat

edkII requires ImageMagick's `convert` to compile.  The
`graphicsmagick-imagemagick-compat` package provides `convert` without
the full ImageMagick library.

Change-Id: I8fc01526842eb408b0015c0652043c20f826a015
Signed-off-by: Tom Hiller <thrilleratplay@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67159
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Michał Żygowski <michal.zygowski@3mdeb.com>

util/docker/coreboot-sdk/Dockerfile

@@ -37,6 +37,7 @@ RUN \
 		git \
 		gnat-12 \
 		golang \
+		graphicsmagick-imagemagick-compat \
 		graphviz \
 		lcov \
 		libcrypto++-dev \