i386/cpu: Fix supervisor xstate initialization

i386/cpu: Fix supervisor xstate initialization

Arch lbr is a supervisor xstate, but its area is not covered in
x86_cpu_init_xsave().

Fix it by checking supported xss bitmap.

In addition, drop the (uint64_t) type casts for supported_xcr0 since
x86_cpu_get_supported_feature_word() returns uint64_t so that the cast
is not needed. Then ensure line length is within 90 characters.

Tested-by: Farrah Chen <farrah.chen@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Co-developed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20251211060801.3600039-10-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>