xen: arm64: more useful logging on bad trap.

xen: arm64: more useful logging on bad trap.

Dump the register state before panicing so we have some clue where the
issue occurred. Also decode the ESR register a bit to save having to
grab a pen and paper.

ESR_EL2 is a 32-bit register, so use SYSREG_READ32 not ..._READ64, as
we already do correctly in the main trap handler.

While here notice that do_trap_serror is never called and remove it.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Julien Grall <julien.grall@linaro.org>
Tested-by: Jintack Lim <jintack@cs.columbia.edu>
Cc: jintack@cs.columbia.edu
[ ijc -- add missing \n to first printk ]