ARM: dts: Properly configure dra7 edma sysconfig registers

Looks like the TRM is not listing the sysconfig for edma, let's add it
based on am437x TRM edma registers as listed in sections "Table 10-26.
EDMA3CC Registers" and "Table 10-99. EDMA3TC Registers".

Tested-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>