ARM: mxc91231: select MXC_AVIC

This fixes:

	arch/arm/kernel/built-in.o: In function `__irq_svc':
	io.c:(.text+0x2e0): undefined reference to `avic_base'
	arch/arm/kernel/built-in.o: In function `__irq_usr':
	io.c:(.text+0x4c8): undefined reference to `avic_base'
	arch/arm/mach-mxc91231/built-in.o: In function `mxc91231_init_irq':
	magx-zn5.c:(.init.text+0x18): undefined reference to `mxc_init_irq'

and was broken by

	c7259df3 (ARM i.MX irq: Compile avic irq code only on SoCs that need it)

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>