target/i386: Change unavail from u32 to u64

target/i386: Change unavail from u32 to u64

The feature word 'r' is a u64, and "unavail" is a u32, the operation
'r &= ~unavail' clears the high 32 bits of 'r'. This causes many vmx cases
in kvm-unit-tests to fail. Changing 'unavail' from u32 to u64 fixes this
issue.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2442
Fixes: 0b2757412cb1 ("target/i386: drop AMD machine check bits from Intel CPUID")
Signed-off-by: Xiong Zhang <xiong.y.zhang@linux.intel.com>
Link: https://lore.kernel.org/r/20240730082927.250180-1-xiong.y.zhang@linux.intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>