bus: ti-sysc: Handle devices with no control registers

Some interconnect target modules have no module control registers at
all, such as d_can on am335x and am437x.

The d_can register offset at 0 is CTL register with 0x401 as the default
value. I guess I mistook the 0x401 value for a revision register as the
value happens to look similar to what the revision registers typically
have for other modules.

To handle modules with no control registers, we need to improve the
ti-sysc driver a bit to bail out with errors on no control registers,
and then we can remove the bogus revision registers for d_can.

Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>