dma: edma: add device_slave_sg_limits() support

Implement device_slave_sg_limits().

EDMA has a finite set of PaRAM slots available for linking a
multi-segment SG transfer. In order to prevent any one channel
from consuming all PaRAM slots to fulfill a large SG transfer,
the driver reports a static per-channel max number of SG segments
it will handle.

The maximum size of an SG segment is limited by the addr_width
and maxburst of a given transfer request. These values are
provided by the client driver and used to calculate and return
the maximum segment length.

[Joel Fernandes <joelf@ti.com>: Changes for filling sg_limits
by DMAEngine implementation and allocating in client, channel
parameter is unused in this implementation as all channels
have the same capability]
Signed-off-by: Matt Porter <mporter@ti.com>
Signed-off-by: Joel A Fernandes <joelagnel@ti.com>
Signed-off-by: Joel Fernandes <joelf@ti.com>