sh: intc - convert voyagergx code

This patch converts the sh-specific voyagergx interrupt code to make use
of intc. A lot of "interesting" old cruft gets replaced with intc tables
and some simple demux code.

- All interrupt sources in the sm501 data sheet are now in the header.
- The number and order of IRQ values are disconnected from register bits.
- Interrupt sources now start from IRQ 200.
- set_irq_chained_handler() is now used to hook up the demux function.

In the future it would probably make sense to move the interrupt demuxer
into into the mfd driver, but this is probably a nice step in the right
direction until that happens.

Tested on a R2D-1 board using the serial port hooked up to the sm501.

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