ARM: OMAP2+: Fix missing select PM_GENERIC_DOMAINS_OF

We should select also PM_GENERIC_DOMAINS_OF in addition to
PM_GENERIC_DOMAINS to have device tree based PM domain providers
enabled.

Fixes: 58cbff02

 ("soc: ti: omap-prm: Add basic power domain support")
Signed-off-by: Tony Lindgren <tony@atomide.com>