clk: renesas: cpg-mssr: Set GENPD_FLAG_ALWAYS_ON for clock domain
The CPG/MSSR Clock Domain driver does not implement the
generic_pm_domain.power_{on,off}() callbacks, as the domain itself
cannot be powered down. Hence the domain should be marked as always-on
by setting the GENPD_FLAG_ALWAYS_ON flag, to prevent the core PM Domain
code from considering it for power-off, and doing unnessary processing.
Note that this only affects RZ/A2 SoCs. On R-Car Gen2 and Gen3 SoCs,
the R-Car SYSC driver handles Clock Domain creation, and offloads only
device attachment/detachment to the CPG/MSSR driver.