Add more BoardConfig variables to stash list

I would like to centralize/standardize the BoardConfig
variable sanity checking in a file similar to product_config.mk,
but for now just add a few more standard BoardConfig
variables to the .KATI_READONLY list.

Also fix the inconsistent indentation in this file.

Test: make
Change-Id: I2a878b95ffc07e3f5bc4eb4970775bdef347e094