sh: intc - convert board specific r2d code

sh: intc - convert board specific r2d code

This patch converts the board specific interrupt code for r2d to make
use of intc. While at it we improve the Kconfig to avoid confusion.

- Two sets of interrupt tables exist - one for R2D-1 and one for R2D-PLUS.
- R2D-1 and R2D-PLUS use the same irq constants.
- R2D-1 has AX88796 support, R2D-PLUS does not hook up that IRQ.
- R2D-PLUS has KEY support, R2D-1 does not hook up that IRQ.
- The number and order of IRQ values are disconnected from register bits.
- Interrupt sources now start from IRQ 100.
- The machvec demux function converts from irlm IRQ 0-14 to IRQ 100++.

Tested on R2D-1 and R2D-PLUS boards.

Version 2 adds CONFIG_RTS7751R2D_1 and CONFIG_RTS7751R2D_PLUS together
with intc structured as __initdata.

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