hw/intc/loongarch_pch: Replace legacy reset callback with new api

hw/intc/loongarch_pch: Replace legacy reset callback with new api

Replace legacy reset callback register device_class_set_legacy_reset()
with new function resettable_class_set_parent_phases(). With new API,
it will call reset callback of parent object.

The internal state has been cleared in parent object
LOONGARCH_PIC_COMMON, here parent_phases.hold() is directly called.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>