Error building zynqmp-fpga.c as a module

zynqmp-fpga-build-error.txt

>>> linux foo-2019.02.26 Building
...
PATH="..." BR_BINARIES_DIR=/home/philip/repos/third-party/buildroot/output/images KBUILD_BUILD_VERSION=1 KBUILD_BUILD_USER=buildroot KBUILD_BUILD_HOST=buildroot KBUILD_BUILD_TIMESTAMP="Tue Jul  9 10:59:29 EDT 2019" KCFLAGS=-Wno-attribute-alias /usr/bin/make -j9 HOSTCC="/home/philip/repos/third-party/buildroot/output/per-package/linux/host/bin/ccache /usr/lib64/ccache/gcc -O2 -I/home/philip/repos/third-party/buildroot/output/per-package/linux/host/include -L/home/philip/repos/third-party/buildroot/output/per-package/linux/host/lib -Wl,-rpath,/home/philip/repos/third-party/buildroot/output/per-package/linux/host/lib" ARCH=arm64 INSTALL_MOD_PATH=/home/philip/repos/third-party/buildroot/output/per-package/linux/target CROSS_COMPILE="/home/philip/repos/third-party/buildroot/output/per-package/linux/host/bin/aarch64-linux-gnu-" DEPMOD=/home/philip/repos/third-party/buildroot/output/per-package/linux/host/sbin/depmod INSTALL_MOD_STRIP=1 -C /home/philip/repos/third-party/buildroot/output/build/linux-foo-2019.02.26 all
make[1]: Entering directory '/home/philip/repos/third-party/buildroot/output/build/linux-foo-2019.02.26'
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CHK     scripts/mod/devicetable-offsets.h
  CHK     include/generated/timeconst.h
  CHK     include/generated/bounds.h
  CHK     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  CHK     include/generated/compile.h
  CHK     kernel/config_data.h
  CC [M]  drivers/fpga/zynqmp-fpga.o
  Building modules, stage 2.
  MODPOST 334 modules
ERROR: "__flush_cache_user_range" [drivers/fpga/zynqmp-fpga.ko] undefined!
make[2]: *** [scripts/Makefile.modpost:92: __modpost] Error 1
make[1]: *** [Makefile:1213: modules] Error 2
make[1]: Leaving directory '/home/philip/repos/third-party/buildroot/output/build/linux-foo-2019.02.26'
make: *** [package/pkg-generic.mk:252: /home/philip/repos/third-party/buildroot/output/build/linux-foo-2019.02.26/.stamp_built] Error 2