s390/entry.S: factor out OUTSIDE macro

Introduce OUTSIDE macro that checks whether an instruction
address is inside or outside of a block of instructions.

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>