Changeset 41 for soft/tp12

Two modifications to better support multi-processors architectures :

1/ The _ioc_read() and _ioc_write() functions have been modified
to use the LL/SC instructions when trying to get the _ioc_busy lock.
This was mandatory to share the IOC controler between several processors.

2/ The _fb_read(), _fb_write(), and the _isr_dma have been modified to use
an array of 256 _dma_busy[pid] locks : Each processor must have its own DMA,
controller, as this array is indexed by the proc_id.