MIPS: xilfpga: Removed unused header files

Header in directory asm/mach-xilfpga is not used any more.
Remove it here, and it passes to compile with xilfpga_defconfig
Signed-off-by: bibo mao <maobibo@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/mach-xilfpga/irq.h

-/* SPDX-License-Identifier: GPL-2.0-or-later */
-/*
- * Copyright (C) 2015 Imagination Technologies
- * Author: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
- */
-
-#ifndef __MIPS_ASM_MACH_XILFPGA_IRQ_H__
-#define __MIPS_ASM_MACH_XILFPGA_IRQ_H__
-
-#define NR_IRQS 32
-
-#include <asm/mach-generic/irq.h>
-
-#endif /* __MIPS_ASM_MACH_XILFPGA_IRQ_H__ */