[kernel] Replace buffer_cache with vm_area_buffers

In order to reduce the amount of tracked state, now use the
vm_area_buffers instead of a VMA with buffer_cache on top.

modules.yaml

@@ -48,7 +48,6 @@ modules:
             - src/kernel/scheduler.cpp
             - src/kernel/screen.cpp
             - src/kernel/serial.cpp
-            - src/kernel/buffer_cache.cpp
             - src/kernel/symbol_table.cpp
             - src/kernel/syscall.cpp
             - src/kernel/syscall.s