Instead of manually calling cpu_x86_set_cpl() when the CPL changes,
check for CPL changes on calls to cpu_x86_load_seg_cache(R_CS).  Every
location that called cpu_x86_set_cpl() also called
cpu_x86_load_seg_cache(R_CS), so cpu_x86_set_cpl() is no longer
required.

This fixes the SMM handler code as it was not setting/restoring the
CPL level manually.
Signed-off-by: NKevin O'Connor <kevin@koconnor.net>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>