ARM: plat-versatile: move FPGA irq driver to drivers/irqchip

This moves the Versatile FPGA interrupt controller driver, used in
the Integrator/AP, Integrator/CP and some Versatile boards, out
of arch/arm/plat-versatile and down to drivers/irqchip where we
have consensus that such drivers belong. The header file is
consequently moved to <linux/platform_data/irq-versatile-fpga.h>.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>