xen/arm: traps: Merge do_trap_instr_abort_guest and do_trap_data_abort_guest

xen/arm: traps: Merge do_trap_instr_abort_guest and do_trap_data_abort_guest

The two helpers do_trap_instr_abort_guest and do_trap_data_abort_guest
are used trap stage-2 abort. While the former is only handling prefetch
abort and the latter data abort, they are very similarly and does not
warrant to have separate helpers.

For instance, merging the both will make easier to maintain stage-2 abort
handling. So consolidate the two helpers in a new helper
do_trap_stage2_abort.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>