EDMA: remove "in_use" field

Remove some significant duplication:

 - We only need a single bitmap to record which PARAM slots are
   in use, and it only needs to have enough bits to cover the
   slots that exist.

 - By using the atomic bitops for that, we eliminate the current
   need for a private spinlock.

 - We don't need to record 'tcc' either, it's only needed inside
   davinci_request_dma().  Remove it:  be clearer and more correct
   (it can change with PARAM operations), save space.

This change highlighted some existing bugs in terms of fault returns
when davinci_request_dma() couldn't return a resource of the relevant
type; unlikely for anyone to have hit them, so far.

Switch to standard kerneldoc for davinci_request_dma().  The two
previous descriptive comments were inconsistent, so fix that too.
Explain the callback usage a bit.

Minor new feature:  allow explicit allocation of slave channels too,
allowing pre-allocation of *any* DMA channel on behalf of DSP code.

This saves about 2 KB of space (half is data) as well as making
allocation and deallocation code a LOT simpler.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>

arch/arm/mach-davinci/include/mach/edma.h

@@ -187,38 +187,6 @@ enum sync_dimension {
 	ABSYNC = 1
 };
 
-/******************************************************************************
- * davinci_request_dma - request for the Davinci DMA channel
- *
- * dev_id - DMA channel number
- *
- * EX: DAVINCI_DMA_MCBSP_TX - For requesting a DMA MasterChannel with MCBSP_TX
- *     event association
- *
- *     DAVINCI_DMA_ANY - For requesting a DMA Masterchannel which does not has
- *     event association
- *
- *     DAVINCI_DMA_LINK - for requesting a DMA SlaveChannel
- *
- * dev_name   - name of the dma channel in human readable format
- * callback   - channel callback function (valied only if you are requesting
- *              for a DMA MasterChannel)
- * data       - private data for the channel to be requested
- * lch        - contains the device id allocated
- * tcc        - specifies the channel number on which the interrupt is
- *              generated
- *              Valied for QDMA and PARAM channes
- * eventq_no  - Event Queue no to which the channel will be associated with
- *              (valied only if you are requesting for a DMA MasterChannel)
- *              Values : EVENTQ_0/EVENTQ_1 for event queue 0/1.
- *                       EVENTQ_DEFAULT for Default queue
- *
- * Return: zero on success,
- *         -EINVAL - if the requested channel is not supported on the ARM side events
- *         -EBUSY - if the requested channel is already in use
- *          EREQDMA - if failed to request the dma channel
- *
- *****************************************************************************/
 int davinci_request_dma(int dev_id,
 			const char *dev_name,
 			void (*callback) (int lch, unsigned short ch_status,