ARM: dts: k2e: Replace 'ti,syscon-psc' property in DSP node

Replace the custom 'ti,syscon-psc' property used for representing
device resets with a DT standard 'resets' property in the DSP node
present within the Keystone 2 Edison SoC. The 'ti,syscon-psc'
property is deprecated, and will not be supported anymore.

Signed-off-by: Andrew F. Davis <afd@ti.com>
[s-anna@ti.com: update commit description]
Signed-off-by: Suman Anna <s-anna@ti.com>