Mount binderfs

Mount binderfs at /dev/binderfs. Also add symlinks from /dev/binder,
/dev/hwbinder and /dev/vndbinder to /dev/binderfs/binder,
/dev/binderfs/hwbinder and /dev/binderfs/vndbinder respectively.

The symlink commands will fail harmlessly on a kernel
which does not support binderfs since /dev/{binder,hwbinder,vndbinder}
devices will exist on the same.

Bug: 136497735
Bug: 148696163

Test: Cuttlefish boots on Android Common Kernel 4.19 with kernel config
CONFIG_ANDROID_BINDERFS=y.

Change-Id: I8e04340dc4622b0a3c1fc4aa6bbefcb24eefe00b