ARM: OMAP2+: DMA: Provide dma_slave_map to omap-dma for legacy boot

We still have some boards booting in legacy mode and they will need to have
the device/slave -> filter_fn mapping so we can convert the OMAP drivers
to use the new dmaengine API for requesting channels.
Only some OMAP24xx and OMAP3xxx boards can boot in legacy mode which means
we only need to provide the map for these SoCs.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>