ARM: dts: dra7: Add nodes for McASP1/2/4/5/6/7/8

Add nodes to represent all McASP ports in the dra7 family.
For system consistency use the eDMA for audio operations. sDMA would be
fine for 4/5/6/7/8 since their DAT port is not through L3 interconnect.

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