x86/vPIC: avoid speculative out of bounds accesses

x86/vPIC: avoid speculative out of bounds accesses

Array indexes used in the I/O port read/write emulation functions are
derived from guest controlled values. Where this is not already done,
restrict their ranges to limit the side effects of speculative execution.

This is part of the speculative hardening effort.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>