refactor(xilinx): create generic function for clock retrieval

Refactors the code in the AMD-Xilinx platform for Versal and Versal NET
to create a more generic function for obtaining clock signals
from the platform. The new function  get_uart_clk is specific to each
platform and providing greater flexibility for clock signal retrieval
in various parts of the codebase.

Signed-off-by: Prasad Kummari <prasad.kummari@amd.com>
Change-Id: Iff67315339b2651c9bea73af0d89fcbad2bb332a
6 files changed