Export 16kb kernel board config variables to soong

These will be used to install the 16kb kernel modules in the soong
autogenerated vendor_dlkm partition.

Test: lunch husky-trunk_staging-userdebug
Test: m soong_generated_vendor_dlkm_filesystem_test
(prints fewer diffs with this change)
Bug: 420669218

Change-Id: I655c07bf65607c5730f9ac444cdded0c240b1929