irqchip/goldfish-pic: Select GENERIC_IRQ_CHIP to fix build

irq-goldfish-pic uses GENERIC_IRQ_CHIP interfaces so select that symbol
to fix build errors.

Fixes these build errors:

mips-linux-ld: drivers/irqchip/irq-goldfish-pic.o: in function `goldfish_pic_of_init':
irq-goldfish-pic.c:(.init.text+0xc0): undefined reference to `irq_alloc_generic_chip'
mips-linux-ld: irq-goldfish-pic.c:(.init.text+0xf4): undefined reference to `irq_gc_unmask_enable_reg'
mips-linux-ld: irq-goldfish-pic.c:(.init.text+0xf8): undefined reference to `irq_gc_unmask_enable_reg'
mips-linux-ld: irq-goldfish-pic.c:(.init.text+0x100): undefined reference to `irq_gc_mask_disable_reg'
mips-linux-ld: irq-goldfish-pic.c:(.init.text+0x104): undefined reference to `irq_gc_mask_disable_reg'
mips-linux-ld: irq-goldfish-pic.c:(.init.text+0x11c): undefined reference to `irq_setup_generic_chip'
mips-linux-ld: irq-goldfish-pic.c:(.init.text+0x168): undefined reference to `irq_remove_generic_chip'

Fixes: 4235ff50

 ("irqchip/irq-goldfish-pic: Add Goldfish PIC driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Miodrag Dinic <miodrag.dinic@mips.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Goran Ferenc <goran.ferenc@mips.com>
Cc: Aleksandar Markovic <aleksandar.markovic@mips.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210905162519.21507-1-rdunlap@infradead.org