ARM: kprobes: Decode 16-bit Thumb branch instructions

We previously changed the behaviour of probes so that conditional
instructions don't fire when the condition isn't met. For ARM branches,
and Thumb branches in IT blocks, this means they don't fire if the
branch isn't taken.

For consistency, we implement the same for Thumb conditional branch
instructions. This involves setting up insn_check_cc to point to the
relevant condition checking function. As the emulation routine is only
called when this condition passes, it doesn't need to check again and
can unconditionally update PC.

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>