ARM: at91: enclose at91_aic_xx calls in IS_ENABLED(CONFIG_OLD_IRQ_AT91) blocks

Enclose at91_aic_xx calls in IS_ENABLED(CONFIG_OLD_IRQ_AT91) blocks in
order to prepare migration to the new AIC driver.

In the new AIC driver the suspend/resume functions are called by the
generic irq framework and are no longer needed in the PM specific code.

Moreover, the new AIC driver no longer exposes the at91_aic_base variable
which is used by the at91_aic_read functions.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>