dt-bindings: clock: ast2600: Add top-level I3C clock

dt-bindings: clock: ast2600: Add top-level I3C clock

The ast2600 hardware has a top-level clock for all i3c controller
peripherals (then gated to each individual controller), so add a
top-level i3c clock line to control this.

This is a partial cherry-pick and rework of ed44b8cdfdb and 1a35eb926d7
from Aspeed's own tree, originally by Dylan Hung
<dylan_hung@aspeedtech.com>.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://lore.kernel.org/r/20230302005834.13171-3-jk@codeconstruct.com.au
Tested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>