um: Set HAVE_EFFICIENT_UNALIGNED_ACCESS for x86

The x86 port of UM has efficient unaligned access. Set the option as it
is appropriate and will e.g. cause UBSAN to not enable unaligned memory
access checking by default.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20240913134442.967599-6-benjamin@sipsolutions.net


Signed-off-by: Johannes Berg <johannes.berg@intel.com>