Add symlink for system_dlkm modules

Create symlinks for system_dlkm on devices with a
system_dlkm partition:

/system/lib/modules -> /system_dlkm/lib/modules

Bug: 200082547
Test: Manual boot with CF
Signed-off-by: Ramji Jiyani <ramjiyani@google.com>
Change-Id: I8ddf340425cf92aa234f93f6b31bfd51cfa9c3f3