sh: clean up interrupt code for solution engine 7722 board

This patch cleans up solution engine 7722 specific interrupt code.
The main purpose is to replace the mux function with use of
set_irq_chained_handler() and replace hard coded register poking
code with set_irq_type(). The board specific interrupts are also
moved to start from SE7722_FPGA_IRQ_BASE.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>