arm64: defconfig: enable SL28VPD NVMEM layout

The Kontron sl28 board is supported upstream and also tested in the
KernelCI. Enable support for its VPD EEPROM where the base ethernet
address is stored.

Signed-off-by: Michael Walle <mwalle@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>