sh: Avoid using IRQ0 on SH3 and SH4

IRQ0 is no longer returned by platform_get_irq() and its ilk -- they now
return -EINVAL instead.  However, the kernel code supporting SH3/4-based
SoCs still maps the IRQ #s starting at 0 -- modify that code to start the
IRQ #s from 16 instead.

The patch should mostly affect the AP-SH4A-3A/AP-SH4AD-0A boards as they
indeed are using IRQ0 for the SMSC911x compatible Ethernet chip.

Fixes: ce753ad1 ("platform: finally disallow IRQ0 in platform_get_irq() and its ilk")
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/71105dbf-cdb0-72e1-f9eb-eeda8e321696@omp.ru


Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>