ARM: dts: dra76x: Disable rtc target module

rtc is fused out on dra76 and accessing target module
register is causing a boot crash hence disable it.

Fixes: 549fce06 ("ARM: dts: dra7: Add l4 interconnect hierarchy and ti-sysc data")
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>