ARM: s3c24xx: convert to sparse-irq

As a final bit of preparation for converting to ARCH_MULTIPLATFORM,
change the interrupt handling for s3c24xx to use sparse IRQs.

Since the number of possible interrupts is already fixed and relatively
small per chip, just make it use all legacy interrupts preallocated
using the .nr_irqs field in the machine descriptor, rather than actually
allocating domains on the fly.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>