Blackfin: use generic name for EVT14 handler

The purpose of the EVT14 handler may depend on whether CONFIG_IPIPE is
enabled, albeit its implementation can be the same in both cases. When
the interrupt pipeline is enabled, EVT14 can be used to raise the core
priority level for the running code; when CONFIG_IPIPE is off, EVT14
can be used to lower this level before running softirq handlers.

Rename evt14_softirq to evt_evt14 to pick an identifier that fits
both, which allows to reuse the same vector setup code as well.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>