target/i386/mshv: fix various cpuid traversal bugs

- Hardcoded max_leaf was not accurate. We query leaf 0x0 and 0x80000000 to
  get the actual max leaves

- On all 0 zeroes on leaf 0x0d, we register 0-63 subleaves with zeros
  indicating XSAVE is disabled

- Subleaf 0 was hardcoded, so the Hypervisor returned defaults for other
  subleaves

- Subleaf 0 was hardcoded, so we were passing 0 instead of actual subleaf
  when adding entries. We now pass the correct subleaf value to
  add_cpuid_entry()

- Leaves 0x04,0x07,0d,0f,10 weren't marked as subleaf-specific

Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
Acked-by: Wei Liu <wei.liu@kernel.org>
Reviewed-by: Doru Blânzeanu <dblanzeanu@linux.microsoft.com>
Link: https://lore.kernel.org/r/20260416121116.527927-4-magnuskulke@linux.microsoft.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>