kvm-unit-test: disable syscall test in 32 bit mode

Fix this error on 32 bit systems:
x86/msr.c:122:5: error: unknown register name ‘r11’ in ‘asm’

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>