habanalabs: remove generic gaudi get_pll_freq function

As we only fetch the CPU_PLL frequency in gaudi, we don't need a
generic get_pll_frequency function which takes a pll index as input

Signed-off-by: Alon Mizrahi <amizrahi@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>