ld-config: Export android.hidl.memory@1.0-impl

This commit exports android.hidl.memory@1.0-impl.so from default linker
namespace to vndk (VNDK-SP) linker namespace.  This fixes
libhidlmemory.so failure.

Note: Exposing android.hidl.memory@1.0-impl.so from default linker
namespace to vndk (VNDK-SP) linker namespace shall be fine because its
APIs are frozen and won't be changed in the future.

Note: android.hidl.memory@1.0-impl.so is NOT exported to sphal linker
namespace.

Bug: 35107583
Bug: 62778280
Test: Write a test SP-HAL lib which links libhidlmemory.so, load that
SP-HAL lib into system executable, and make sure mapMemory() works.
Test: sailfish boots w/o problems.

Change-Id: Ia36350dcf1f8c8dc6d7bf2c7a6ae65e0ebaef578