ARM: dts: dra7: Add syscon regmap for CORE CONTROL area

Display and DCAN drivers use syscon regmap to access some registers
in the CORE control area. Add the syscon regmap node for this
area.

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Nishanth Menon <nm@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>