ARM: DRA7: hwmod: Do not register RTC on DRA71

RTC is not available on DRA71x, so accessing any of the RTC
register or clkctrl register will lead to a crash. So, do not
register RTC hwmod for DRA71x.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>