The differences from ARMv7-M NVIC are:
* ARMv6-M only supports up to 32 external interrupts
(configurable feature already). The ICTR is reserved.
* Active Bit Register is reserved.
* ARMv6-M supports 4 priority levels against 256 in ARMv7-M.
Signed-off-by: Julia Suvorova <jusual@mail.ru>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
c4379b4874