xen: arm: handle remaining traps from userspace

xen: arm: handle remaining traps from userspace

CP14 dbg and general CP register access are both handled with
unconditional injection of #undef from their respective handlers, so
allow these even from 32-bit userspace on a 64-bit kernel.

SMC32 and HVC32 should only come from a guest in AArch32 mode and
SMC64 and HVC64 should only come from a guest in AArch64 mode. Add
appropriate BUG_ONs to all cases.

After this bad_trap is no longer used.

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