ARM: at91: fix build breakage due to legacy board removals

Fixes the following missing includes:

arch/arm/mach-at91/at91sam9g45.c: In function 'at91sam9g45_init_time':
arch/arm/mach-at91/at91sam9g45.c:39:23: error: 'NR_IRQS_LEGACY' undeclared (first use in this function)
  at91sam926x_pit_init(NR_IRQS_LEGACY + AT91_ID_SYS);
                       ^
arch/arm/mach-at91/at91sam9g45.c:39:23: note: each undeclared identifier is reported only once for each function it appears in
make[3]: *** [arch/arm/mach-at91/at91sam9g45.o] Error 1
arch/arm/mach-at91/at91sam9rl.c: In function 'at91sam9rl_init_time':
arch/arm/mach-at91/at91sam9rl.c:51:23: error: 'NR_IRQS_LEGACY' undeclared (first use in this function)
  at91sam926x_pit_init(NR_IRQS_LEGACY + AT91_ID_SYS);

Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Olof Johansson <olof@lixom.net>