and avoid to define .nr_irqs in your machine,
the first 16 IRQs will be pre-allocated, and the IRQdomain
code (as the VIC core code before it) will then assume
that all IRQ descriptors are pre-allocated, and 16 of them
are - by somebody else. So mapping the IRQs will fail in
irq_create_mapping(). Moving the offset upward rids us of
this problem.

Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>