winsup/cygwin/fhandler/proc.cc: format_proc_cpuinfo() Linux 6.8 cpuinfo flags

winsup/cygwin/fhandler/proc.cc: format_proc_cpuinfo() Linux 6.8 cpuinfo flags

add Linux 6.8 cpuinfo flags:
Intel 0x00000007:1 eax:17 fred		Flexible Return and Event Delivery;
AMD   0x8000001f   eax:4  sev_snp	SEV secure nested paging;
document unused and some unprinted bits that could look like omissions;
fix typos and misalignments;

Signed-off-by: Brian Inglis <Brian.Inglis@SystematicSW.ab.ca>