i386/machine: Use VMSTATE_UINTTL_SUB_ARRAY for vmstate of CPUX86State.regs

i386/machine: Use VMSTATE_UINTTL_SUB_ARRAY for vmstate of CPUX86State.regs

Before expanding the number of elements in the CPUX86State.regs array,
first use VMSTATE_UINTTL_SUB_ARRAY for the regs' vmstate to avoid the
type_check_array failure.

VMSTATE_UINTTL_SUB_ARRAY will also be used for subsequently added elements
in regs array.

Tested-by: Xudong Hao <xudong.hao@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20251211070942.3612547-3-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>