pldm: use 'libpldm-only' option

A compile failure in pldm due to a change in phosphor-dbus-interfaces
broke all of CI.  pldm is imported into our build-unit-test-docker
script because it provides a shared library currently used by
phosphor-debug-collector.  I requested this dependency be removed with
openbmc/openbmc#3749, but in the meantime we should utilize the
`libpldm-only` feature to decrease the surface area of compile fails.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I4deaff23327c9e5d32da65a4966c01982c99e909
diff --git a/build-unit-test-docker.sh b/build-unit-test-docker.sh
index 12e90fc..01c4346 100755
--- a/build-unit-test-docker.sh
+++ b/build-unit-test-docker.sh
@@ -496,7 +496,7 @@
 COPY --from=openbmc-CLI11 ${PREFIX} ${PREFIX}
 RUN curl -L https://github.com/openbmc/pldm/archive/${PKG_REV['openbmc/pldm']}.tar.gz | tar -xz && \
 cd pldm-* && \
-meson build ${MESON_FLAGS[@]} -Dtests=disabled && \
+meson build ${MESON_FLAGS[@]} -Dlibpldm-only=enabled -Dtests=disabled && \
 ninja -C build && \
 ninja -C build install