irqchip/gic-pm: Remove PM_CLK dependency

gic-pm driver does not use pm-clk interface now and hence the dependency
is removed from Kconfig.

Signed-off-by: Sameer Pujar <spujar@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>