plat: xilinx: versal: Add support to get clock rate value

Add support to get clock's rate value.

Signed-off-by: Tejas Patel <tejas.patel@xilinx.com>
Signed-off-by: Rajan Vaja <rajan.vaja@xilinx.com>
Change-Id: I3ed881053ef323b2ca73e13edd0affda860d381d
3 files changed