bus: ti-sysc: Improve reset to work with modules with no sysconfig

[ Upstream commit ab4d309d8708035bd323b2e2446eb68cda5e61e5 ]

At least display susbsystem (DSS) has modules with no sysconfig registers
and rely on custom function for module reset handling. Let's make reset
work with that too.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Stable-dep-of: 34539b442b3b ("bus: ti-sysc: Flush posted write on enable before reset")
Signed-off-by: Sasha Levin <sashal@kernel.org>