ARM: at91: fix new build errors

MULTI_IRQ_HANDLER and SPARSE_IRQ are now required everywhere because
mach/irqs.h and mach/entry-macros.S are gone but the symbols are
only selected for AT91SAM9, not for the NOMMU parts.

A few files now need to include linux/io.h directly, which used to
be included through other headers that have changed.

The new at91_aic_irq_priorities variable is only used with CONFIG_OF
enabled and should not be visible otherwise.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>