kernel: Use nproc from prebuilts

Change-Id: I1d7a33dac57cbba9ce1a92f81d74709146e92968
diff --git a/config/BoardConfigKernel.mk b/config/BoardConfigKernel.mk
index f782074..e6dee41 100644
--- a/config/BoardConfigKernel.mk
+++ b/config/BoardConfigKernel.mk
@@ -117,7 +117,7 @@
 KERNEL_MAKE_FLAGS :=
 
 # Add back threads, ninja cuts this to $(nproc)/2
-KERNEL_MAKE_FLAGS += -j$(shell nproc --all)
+KERNEL_MAKE_FLAGS += -j$(shell prebuilts/tools-lineage/$(HOST_PREBUILT_TAG)/bin/nproc --all)
 
 ifeq ($(KERNEL_ARCH),arm)
   # Avoid "Unknown symbol _GLOBAL_OFFSET_TABLE_" errors