clk: ast2600: Add comment about combined clock + reset handling

clk: ast2600: Add comment about combined clock + reset handling

Add a little description about how reset lines can be implicit with
clock enable/disable. This is mostly based on the commit message
from the original submission in 15ed8ce5f8.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://lore.kernel.org/r/20230302005834.13171-6-jk@codeconstruct.com.au
Reviewed-by: Joel Stanley <joel@jms.id.au>
Tested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>