zynqmp: pm: Add API to get number of clocks

zynqmp: pm: Add API to get number of clocks

Currently in Linux maximum number of clocks is hard-coded and
so it needs to allocate static memory. It can get actual clock
number after querying all clock names by special clock name
string. Add new query data parameter to get actual number of
clocks so Linux can get actual clock numbers in advance.

Signed-off-by: Rajan Vaja <rajan.vaja@xilinx.com>