ARM: dts: DRA74x: Add DSP2 processor device node

The DRA7xx family of SoCs can contain upto two identical DSP
processor subsystems. The second DSP processor subsystem is
present only on the DRA74x/DRA76x variants. The processor
device DT node has therefore been added in disabled state for
this processor subsystem in the DRA74x specific DTS file.

NOTE:
1. The node does not have any mailboxes, timers or CMA region
   assigned, they should be added in the respective board dts
   files.
2. The node should also be enabled as per the individual product
   configuration in the corresponding board dts files.

Signed-off-by: Suman Anna <s-anna@ti.com>
[t-kristo@ti.com: converted to support ti-sysc from legacy hwmod]
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>