This completes the simplification work by dedicating calls to resume
and thread from a forcible stop (T_SUSP, T_HALT, T_INBAND and
T_DORMANT), and event-bounded waits.

For consistency purpose, the related calls have been renamed:
evl_{hold, release}_thread() control the forcible stop states, while
evl_{sleep_on, wakeup}_thread() control the event wait states.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>