Revert "Some changes to kernel.mk"

This reverts commit 842393197de8c323b773c2bc55ef70229c7a39ea.
Revert "Fix vendor path"

This reverts commit cb011606875175c96b6fec219438543446f2540b.
Revert "build: Fix kernel.mk typos"

This reverts commit 702595df77d4262a6e7eb8ad91b75e8d0d3a2af9.
Revert "build: Inline kernel building as a buildtime task"

This reverts commit f3de7b7a2e06fc58ed41fc2353356945ac911073.