target/i386: fix xsave.flat from kvm-unit-tests

target/i386: fix xsave.flat from kvm-unit-tests

xsave.flat checks that "executing the XSETBV instruction causes a general-
protection fault (#GP) if ECX = 0 and EAX[2:1] has the value 10b".  QEMU allows
that option, so the test fails.  Add the condition.

Cc: qemu-stable@nongnu.org
Fixes: 892544317fe ("target/i386: implement XSAVE and XRSTOR of AVX registers", 2022-10-18)
Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 7604bbc2d87d153e65e38cf2d671a5a9a35917b1)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>