x86: Clean up the global, page_table_levels, in access.c

Remove the global, page table levels, from access.c and store it in the
test struct ac_test_t instead.

Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Message-Id: <20211110212001.3745914-14-aaronlewis@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>