fix(psci): fix parent_idx in psci_validate_state_coordination

Update parent_idx support in psci_validate_state_coordination() as
it is done in psci_do_state_coordination(). The modified loop verifies
the targeted state for all the branch up to end_pwrlvl in the topology
for the current cpu.

Fixes: 606b7430 ("feat(psci): add support for OS-initiated mode")
Change-Id: I14420f64a18b543eb4e10a1279f51cc17558c13c
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>