Install LOCAL_SOONG_INSTALL_SYMLINKS even if LOCAL_SOONG_INSTALLED_MODULE isn't set

LOCAL_SOONG_INSTALL_SYMLINKS can now be set by the install_symlink
module type. The install_symlink module type doesn't set
LOCAL_SOONG_INSTALLED_MODULE because make tries to copy that file
around, which doesn't work with a symlink.

Bug: 205632228
Test: built and ran the emulator observed the /system/bin/hwservicemanager symlink is still there
Change-Id: I1ec355b5ae057d0b7fe167674d70da6a4d03f6b5