dmaengine: at_hdmac: Use bitfield access macros

Use the bitfield access macros in order to clean and to make the driver
easier to read. One will see some "line length exceeds 100 columns"
checkpatch warnings. I chose to not introduce new lines for regs
descriptions in order to preserve the style of the comments throughout
the definitions. Style can be fixed in a further patch.
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20221025090306.297886-1-tudor.ambarus@microchip.com
Link: https://lore.kernel.org/r/20221025090306.297886-29-tudor.ambarus@microchip.comSigned-off-by: Vinod Koul <vkoul@kernel.org>