clk: renesas: rzg2l: Add support for MSTOP in clock enable/disable API

The RZ/{G2L,V2L,G3S} CPG versions support a feature called MSTOP.  Each
module has one or more MSTOP bits associated with it, and these bits
need to be configured along with the module clocks. Setting the MSTOP
bits switches the module between normal and standby states.

Previously, MSTOP support was abstracted through power domains (struct
generic_pm_domain::{power_on, power_off} APIs).  With this abstraction,
the order of setting the MSTOP and CLKON bits was as follows:

Previous Order:
A/ Switching to Normal State (e.g., during probe):
1/ Clear module MSTOP bit
2/ Set module CLKON bit

B/ Switching to Standby State (e.g., during remove):
1/ Clear CLKON bit
2/ Set MSTOP bit

However, in some cases (when the clock is disabled through devres), the
order may have been (due to the issue described in link section):

1/ Set MSTOP bit
2/ Clear CLKON bit

Recently, the hardware team has suggested that the correct order to set
the MSTOP and CLKON bits is:

Updated Order:
A/ Switching to Normal State (e.g., during probe):
1/ Set CLKON bit
2/ Clear MSTOP bit

B/ Switching to Standby State (e.g., during remove):
1/ Set MSTOP bit
2/ Clear CLKON bit

To prevent future issues due to incorrect ordering, the MSTOP setup has
now been implemented in rzg2l_mod_clock_endisable(), ensuring compliance
with the sequence suggested in Figure 41.5: Module Standby Mode
Procedure from the RZ/G3S HW manual, Rev1.10.

Additionally, since multiple clocks of a single module may be mapped to
a single MSTOP bit, MSTOP setup is reference-counted.

Furthermore, as all modules start in the normal state after reset, if
the module clocks are disabled, the module state is switched to standby.
This prevents keeping the module in an invalid state, as recommended by
the hardware team.

Link: https://lore.kernel.org/all/20250215130849.227812-1-claudiu.beznea.uj@bp.renesas.com/
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20250527112403.1254122-5-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

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