Platform/NXP/LS1043aRdbPkg: Add Clock retrieval APIs

The SOC takes primary clocking input from the external signal (a clock
generator on board). The input (frequency) is multiplied using multiple
phase locked loops (PLL) to create a variety of frequencies which can
then be passed to a variety of internal logic, including cores and
peripheral IP modules.

Therefore, move the clock retrieval APIs to Platform Lib.
The Input clock is retrieved from board components in Platform Lib, and
passed on to SOC Lib APIs to get the correct clock for an IP (after PLL
multiplication).

Signed-off-by: Pankaj Bansal <pankaj.bansal@nxp.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>