hw/intc/loongarch_pch_msi: Remove gpio input handler

hw/intc/loongarch_pch_msi: Remove gpio input handler

MSI interrupt is triggered by writing message on specified memory address.
In generic it is used by PCI devices, and no device is connected pch MSI
irqchip with GPIO pin line method, here remove gpio input setting for MSI
controller.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Tested-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20250410085004.3577627-1-maobibo@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>