The current ast2600 clock definitions include entries for i3c6 and i3c7
devices, which don't exist: there are no clock control lines documented
for these, and only i3c devices 0 through 5 are present.

So, remove the definitions for I3C6 and I3C7. Although this is a
potential ABI-breaking change, there are no in-tree users of these, and
any references would be broken anyway, as the hardware doesn't exist.

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>.
Reviewed-by: Joel Stanley <joel@jms.id.au>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://lore.kernel.org/r/20230302005834.13171-5-jk@codeconstruct.com.auTested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>