blackfin: mach-common: ints-priority: remove unused function

Remove the function bfin_sec_resume() that is not used anywhere.

This was partially found by using a static code analysis program called
cppcheck.

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>