USB: musb: bugfixes for multi-packet TXDMA support

We really want to use DMA mode 1 for all multi-packet transfers;
that's one IRQ on DMA completion, instead of one per packet.

There is an important issue with such transfers, especially on
the host side:  when such transfers end with a full-size packet,
we must defer musb_dma_completion() calls until the FIFO empties.
Else we report URB completions too soon, and may clobber data in
the FIFO fifo when writing the next packet (losing data).

The Inventra DMA support uses DMA mode 1, but it ignores that
issue.  The CPPI DMA support uses mode 0, but doesn't handle
its TXPKTRDY interrupts quite right either; it can get stale
"packet ready" interrupts, and report transfer completion too
early using slightly different code paths, also losing data.

So I'm solving it in a generic way -- by adding a sort of the
"interrupt filter" into musb_host_tx(), catching these cases
where a DMA completion IRQ doesn't suffice and removing some
needlessly controller-specific logic.  When a TXDMA interrupt
happens and DMA request mode 1 is active, that filter resets
to mode 0 and defers URB completion processing until TXPKTRDY,
unless the FIFO is already empty.  Related filtering logic in
Inventra and CPPI code gets removed.

Since it should be competely safe now to use the DMA request
mode 1 for host side transfers with the CPPI DMA controller,
set it in musb_h_tx_dma_start() ... now renamed (and shared).

[ dbrownell@users.sourceforge.net: don't introduce more
CamElCase; use more concise explanations ]

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>