irqchip/ftintc010: Mark all function static

Two functions were always global but never had any callers
outside of this file:

drivers/irqchip/irq-ftintc010.c:128:39: error: no previous prototype for 'ft010_irqchip_handle_irq'
drivers/irqchip/irq-ftintc010.c:165:12: error: no previous prototype for 'ft010_of_init_irq'

Fixes: b4d3053c ("irqchip: Add a driver for Cortina Gemini")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230516200516.554663-1-arnd@kernel.org