mfd: Fix Arizona Kconfig entry

The core and irq Arizona parts should be boolean as they depend on non
exported symbols.

This fixes the following build errors:

ERROR: "wm5102_aod" [drivers/mfd/arizona-irq.ko] undefined!
ERROR: "wm5102_irq" [drivers/mfd/arizona-irq.ko] undefined!
ERROR: "irq_set_chip_and_handler_name" [drivers/mfd/arizona-irq.ko]  undefined!
ERROR: "wm5102_patch" [drivers/mfd/arizona-core.ko] undefined!
ERROR: "arizona_irq_init" [drivers/mfd/arizona-core.ko] undefined!
ERROR: "arizona_irq_exit" [drivers/mfd/arizona-core.ko] undefined!

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>