Add secondary counter in place of tls_nodelete flag

The tls_nodelete state should apply to load_group not
isolated soinfo. This actually also means that multiple
soinfos may have tls_counter on their dso_handles.

This change replaces TLS_NODELETE flag with secondary counter.
Note that access to the secondary counter (located inside soinfo)
is pretty expensive because it requires soinfo lookup by dso_handle
whereas dso_handle counter is much faster. This is why it is updated
only when dso_handle counter starts or hits 0.

Bug: http://b/80278285
Test: bionic-unit-tests --gtest_filter=dl*
Change-Id: I535583f6714e45fa2a7eaf7bb3126da20ee7cba9