add more dirty NIF API functions

Add enif_is_on_dirty_scheduler() and enif_have_dirty_schedulers()
functions. Add calls to them to nif_SUITE dirty NIF test.
fix command-line options for dirty schedulers

Make +SDcpu take a n1:n2 argument for dirty CPU schedulers and dirty CPU
schedulers online, similar to the existing +S option. Add the +SDPcpu
option to allow numbers of dirty CPU schedulers and dirty CPU schedulers
online to be specified as percentages, similar to the existing +SP option.

The number of dirty schedulers defaults to the number of schedulers, and
the number of dirty schedulers online defaults to the number of dirty
schedulers online.

Change erts/configure.in to separate dirty scheduler support from SMP
support. It instead depends only on thread support. Modify erl_bif_info.c
and erl_init.c to start handling this change as well.