arm: traps: handle unknown exceptions in check_conditional_instr()

arm: traps: handle unknown exceptions in check_conditional_instr()

According to ARM architecture reference manual (ARM DDI 0487B.a page D7-2259,
ARM DDI 0406C.c page B3-1426), exception with unknown reason (HSR.EC == 0)
has no valid bits in HSR (apart from HSR.EC), so we can't check if that was
caused by conditional instruction. We need to assume that it is unconditional.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>