KERNDIR setting in OpenEmbedded (core)

I am trying to build kernel driver for e-paper display over SPI bus (GitHub - repk/epd: Epaper Display Linux kernel driver for EM027AS012).
I have successfully build and downloaded latest kernel into my colibri-vf50 using the steps described in (OpenEmbedded (core) - Toradex System/Computer on Modules)
After building and installing the toolchain, I have exported the environment variable and started cross-compile for the github project.

This now reports a missing configuration for kernel.

I would like to keep the kernel configuration during build. Can you please help?

Output of the make command.

make -C /home/me/oe/build/tmp-glibc/work-shared/colibri-vf/kernel-source/ M=/home/me/work/epd/build/epd modules
make[1]: Entering directory '/home/me/oe/build/tmp-glibc/work-shared/colibri-vf/kernel-source'

  ERROR: Kernel configuration is invalid.
         include/generated/autoconf.h or include/config/auto.conf are missing.
         Run 'make oldconfig && make prepare' on kernel src to fix it.

  WARNING: Symbol version dump ./Module.symvers
           is missing; modules will have no dependencies and modversions.

  Building modules, stage 2.
scripts/Makefile.modpost:42: include/config/auto.conf: No such file or directory
make[2]: *** No rule to make target 'include/config/auto.conf'.  Stop.
Makefile:1408: recipe for target 'modules' failed
make[1]: *** [modules] Error 2
make[1]: Leaving directory '/home/me/oe/build/tmp-glibc/work-shared/colibri-vf/kernel-source'
Makefile:40: recipe for target 'default' failed
make: *** [default] Error 2

I guess what you are trying to do is building a so called out of tree module. For this to work with any recent kernel version a fully configured and somewhat even compiled kernel source tree needs to be referenced. Just proceed as per the following article on our developer website prior to what you attempted above.