sh: intc: Add IRQ trigger bit field check

R-Mobile SoCs such as sh73a0 include PINT blocks in INTC
that come with 2-bit IRQ trigger support. Add code to make
sure the bit width is checked so 4-bit only modes like for
instance EDGE_BOTH will fail for PINT.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>