davinci: Keep count of channel controllers on a platform

Some architectures have only one channel controller, but the
edma_alloc_channel api loops twice to findout the free channel
available in EDMA_CHANNEL_ANY case. A new variable has been
introduced to keep count of number of channel controllers being
used on a particular architecture.

Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>