bus: ti-sysc: Add handling for clkctrl opt clocks

There can be up to eight optional device functional gate gate clocks for
each clkctrl instance in clkctrl register bits 8 to 15. Some of them are
only needed for module level reset while others may always be needed
during use. Let's add support for those and update the binding doc
accordingly.

Note that the optional clkctrl mux and divider clocks starting at bit 20
can be directly mapped to the child devices, and ti-sysc does not need to
manage those.

And as GPIOs need the optional clocks for reset, we can now add it with
SYSC_QUIRK_OPT_CLKS_IN_RESET.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Tero Kristo <t-kristo@ti.com>
Cc: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>