[avicii] Kernel fails to build from clean tree due to missing vendor paths

## Affected branch
- Repository: android_kernel_oneplus_sm7250
- Branch: avicii
- Commit: 58460d35bd9e7463df3f81c1dce1c2a0462e8f45

## Description
Building the kernel from a clean clone of this repository fails due to
references to vendor-specific paths that are not present in the source
tree.

This occurs even when using the provided defconfig without any local
modifications.

## Build environment
- Host OS: Linux (WSL2 Ubuntu 22.04)
- Toolchain: AOSP clang 12.0.5
- Target: arm64
- Build commands:

make mrproper
make avicii_defconfig
make -j$(nproc)

## Build error

scripts/Makefile.modbuiltin:26: kernel/sched_assist/Makefile: No such file or directory
scripts/Makefile.modbuiltin:26: kernel/special_opt/Makefile: No such file or directory
make: *** [Makefile:1488: kernel/modules.builtin] Error 2

## Analysis
The build system enables multiple OPLUS_FEATURE_* macros which cause
Makefiles to unconditionally reference the following directories:

- kernel/sched_assist/
- kernel/special_opt/
- kernel/keventupload/

However, these directories do not exist in the public repository.

Even after cleaning (`make mrproper`) and reapplying the defconfig,
the same missing-path errors occur, indicating this is not caused by
local configuration or a stale build.

## Expected behavior
One of the following:
1. The kernel builds successfully from this repository alone, OR
2. Required vendor source overlays are documented, OR
3. The defconfig disables features whose sources are not published

## Question
Is this branch expected to build standalone, or does it rely on
additional internal/vendor source trees that are not part of this
repository?

If the latter, could this be documented in the README or build
instructions?

Thank you.

[OnePlusOSSAdmin]

There are 2 or 3 repositories for one project.
android_kernel_oneplus_sm7250 code to ./kernel/msm-4.19
android_kernel_modules_and_devicetree_oneplus_sm7250 code to ./