Add the clk_branch2_prepare_ops for supporting clock controller
where the hardware register is accessed by MDIO bus, and the
spin lock can't be used because of sleep during the MDIO
operation.

The clock is enabled by the .prepare instead of .enable when
the clk_branch2_prepare_ops is used.
Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Luo Jie <quic_luoj@quicinc.com>
Link: https://lore.kernel.org/r/20240605124541.2711467-2-quic_luoj@quicinc.comSigned-off-by: Bjorn Andersson <andersson@kernel.org>