sh: multiple vectors per irq - sh7750

Update intc tables and platform data to use one linux irq
per maskable interrupt source instead of keeping the one-to-one
mapping between vectors and linux irqs.

This fixes potential irq masking issues for sh775x hardware
blocks such as SCI/SCIF/RTC/DMAC/TMU2/REF.

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