xen: arm: handle traps of conditional instructions.

xen: arm: handle traps of conditional instructions.

This means handling the HSR.ccvalid field as well as correctly processing the
Thumb If-Then state block in the CPSR correctly which is rather tricky. KVM
provided a useful reference for all this.

I suspect we aren't actually hitting these paths very often since the sorts of
traps we take will not often be conditional so my limited testing may not
actually be exercising these paths very much.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Julien Grall <julien.linaro.org>