clk: scmi: add is_prepared hook

clk: scmi: add is_prepared hook

Some clocks maybe default enabled by hardware. For clocks that don't
have users, that will be left in hardware default state, because prepare
count and enable count is zero,if there is no is_prepared hook to get
the hardware state. So add is_prepared hook to detect the hardware
state. Then when disabling the unused clocks, they can be simply
turned OFF to save power during kernel boot.

Reviewed-by: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20240806145601.1184337-1-peng.fan@oss.nxp.com
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>