K2G devices still only use single parameter for power-domains property,
so check for this properly in the driver. Without this, every peripheral
fails to probe resulting in boot failure.

Link: https://lore.kernel.org/r/20201029093337.21170-1-t-kristo@ti.com
Fixes: efa5c01c ("soc: ti: ti_sci_pm_domains: switch to use multiple genpds instead of one")
Reported-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>