mach-k3: refactor A53 speed grade clock-rate fixup

mach-k3: refactor A53 speed grade clock-rate fixup

The K3 ARM64 rproc driver uses the "assigned-clock-rates" value in the
respective "/a53@0" node to properly configure the clocks for the A53
core.

Although the clock value in the DT node might need to be fixed based on
SoC's speed grade at runtime. Certain SoCs such as AM62p and AM62x
already had this implemented, this patch moves the common code to
common.c to avoid duplication and simplify speed grade handling.

The logic to detect the correct entry in the "assigned-clock-rates"
property has also changed. Where we earlier relied on per SoC specific
device and clock IDs for the A53 core, we now use the "clock-names"
property which is device agnostic.

Signed-off-by: Anshul Dalal <anshuld@ti.com>
Reviewed-by: Aniket Limaye <a-limaye@ti.com>