ARM: OMAP2+: DMA: Add slave map entries for 24xx external request lines

The external request lines are used by tusb6010 on OMAP24xx platforms.
Update the map so the driver can use dmaengine API to request the DMA
channel. At the same time add temporary map containing only the external
DMA request numbers for DT booted case on omap24xx since the tusb6010 stack
is not yet supports DT boot.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>