ARM: imx: select USE_OF

ARM: imx: select USE_OF

Commit

      544496a (ARM: imx: move irq_domain_add_legacy call into avic driver)

introduced unconditional calls to irq_find_mapping and
irq_domain_add_legacy, but it's still possible to have a .config without
CONFIG_IRQ_DOMAIN=y resulting in

	  CC      arch/arm/plat-mxc/avic.o
	arch/arm/plat-mxc/avic.c: In function 'avic_handle_irq':
	arch/arm/plat-mxc/avic.c:172: error: implicit declaration of function 'irq_find_mapping'
	arch/arm/plat-mxc/avic.c: In function 'mxc_init_irq':
	arch/arm/plat-mxc/avic.c:207: error: implicit declaration of function 'irq_domain_add_legacy'
	arch/arm/plat-mxc/avic.c:208: error: 'irq_domain_simple_ops' undeclared (first use in this function)
	arch/arm/plat-mxc/avic.c:208: error: (Each undeclared identifier is reported only once
	arch/arm/plat-mxc/avic.c:208: error: for each function it appears in.)
	arch/arm/plat-mxc/avic.c:208: warning: assignment makes pointer from integer without a cast
	make[3]: *** [arch/arm/plat-mxc/avic.o] Error 1
	make[2]: *** [arch/arm/plat-mxc/avic.o] Error 2
	make[1]: *** [sub-make] Error 2
	make: *** [all] Error 2

While selecting CONFIG_IRQ_DOMAIN would be enough, USE_OF is the future
and implies CONFIG_IRQ_DOMAIN. So select USE_OF for ARCH_MXC and drop
other explicit selects that are superflous now.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>