blackfin: Remove exec_domain usage

As execution domain support is gone we can remove
signal translation from the signal code and remove
exec_domain from thread_info.

Signed-off-by: Richard Weinberger <richard@nod.at>

diff --cc arch/blackfin/include/asm/thread_info.h
Simple merge

diff --cc arch/blackfin/kernel/signal.c
Simple merge