BpfLoader: split bpffs subdir creation out am: 7ff8310ea2 am: 9176944a72

Original change: https://android-review.googlesource.com/c/platform/system/bpf/+/3217182

Change-Id: I74ee19fab2931fb51d0666e0c646d550dc9d2011
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>