mach-bcm2708: Reserve 64 IRQs for peripherals

The Raspberry Pi does not support dynamic IRQs.  Some peripherals, such
as the STMPE, add IRQ controllers.  If there aren't any reserved IRQs, then
these peripherals will just fail.

Signed-off-by: Sean Cross <xobs@kosagi.com>
Signed-off-by: Noralf Tronnes <notro@tronnes.org>