clk: zynqmp: Fix clk dump values

With "clk dump" command, few clocks are showing up incorrect values
and some clocks are displayed as "unknown".

Add missing clocks to zynqmp clock driver to display proper
clocks rates.

Implement a simple way to get clock source, instead of calling
functions. Change existing functions to this simple mechanism.

Fix gem clock name "gem_rx" to "gem_tx" which was incorrect.
Change dbf_fpd & dbf_lpd clk names to dbg_fpd & dbg_lpd.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>