powerpc/powernv: Avoid explicit endian conversions while parsing device tree

We currently read the information about idle states from the device
tree, so as to find out the CPU idle states supported by the platform.

Use the of_property_read/count_xxx() APIs, which handle endian
conversions for us, and mean we don't need any endian annotations in the
code.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>