sh: default to sparseirq.

sh: default to sparseirq.

As SH has a very sparse IRQ map by default, all new CPUs and boards
benefit from using sparseirq by default. Despite this, there are still a
few stragglers (mostly due to using a fixed IRQ range for their FPGA
IRQ mappings), and these still need to be converted over one by one. As
these are now in the minority, and we do not want to encourage this sort
of brain-damage in newer board ports, we force sparseirq on.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>