dmaengine: at_hdmac/trivial: correct typo in comment

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
dmaengine: at_hdmac: extend hardware handshaking interface identification

Peripheral handshaking identification numbers can be bigger than 15, so new
fields have been created in the CFG register.
Add macros to take this modification into account and use them in
at_dma_xlate() function.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
dmaengine: at_hdmac/trivial: rearrange CFG register bits assignment

No modification in CFG register configuration, just rearrange
bits directives to group logically and make it more readable.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>