This change fixes a bug where a compiler choses a signed byte
to store the IRQn_Type enum type as all listed enum values
fit a signed byte. This causes undefined behavior when calling
functions such as NVIC_EnableIRQ with interrupt channels greater
than 127 as these do not fit a signed byte. As a result,
interrupt channels higher than 127 cannot be enabled, disabled,
or triggered.

Fix this by listing the highest possible interrupt channel in
each enum declaration which ensures that a storage type is chosen
that can accommodate all valid interrupt channels.

Tested on a MEC1527 devices by triggering interrupt channel
171 (watchdog) and observing that the ISR is executed.