Fix potential build break

When BOARD_PROPERTY_OVERRIDES_SPLIT_ENABLED is enabled, the build system
may attempt to create a symlink in TARGET_ROOT_OUT before TARGET_ROOT_OUT
is created. Also make the symbolic link depend on
INSTALLED_DEFAULT_PROP_TARGET so that the symbolic link is properly created
when only bootimage is made.

Bug: 63645797
Test: on non-A/B device, make installclean && make bootimag and then verify
      that the symbolic link exists at $(TARGET_ROOT_OUT)/default.prop
Change-Id: Id12916b465ff052e2594b79f28274be20ca53af7
Merged-In: I1a9a2ba49c8252afc13ced3dea71253afbd3091e