irqchip/qcom-pdc: Kill qcom_pdc_translate helper

qcom_pdc_translate() really is nothing but an open coded version
of irq_domain_translate_twocell(). Get rid of it and use the common
version instead.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Maulik Shah <quic_mkshah@quicinc.com>
Link: https://lore.kernel.org/r/20220224101226.88373-4-maz@kernel.org