x86emul: replace UB shifts

x86emul: replace UB shifts

Displacement values can be negative, hence we shouldn't left-shift them.
Or else we get

(XEN) UBSAN: Undefined behaviour in x86_emulate/x86_emulate.c:3482:55
(XEN) left shift of negative value -2

While auditing shifts, I noticed a pair of missing parentheses, which
also get added right here.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>
x86: comment update after "drop high compat r/o M2P table address range"

Commit 5af040ef8b57 clearly should also have updated the comment, not
just the #define-s.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: b6a907f8c83d37886d0523f1aeff61b98e133498
master date: 2020-07-31 17:41:58 +0200
master commit: 2e98d0b1d09e99e3d1287cb13f42b604ebc3c29a
master date: 2020-08-05 10:21:22 +0200