x86: Properly match CPU features in /proc/cpuinfo [BZ #27222]

Search " YYY " and " YYY\n", instead of "YYY", to avoid matching
"XXXYYYZZZ" with "YYY".

Update /proc/cpuinfo CPU feature names:

/proc/cpuinfo                     glibc
------------------------------------------------
avx512vbmi                        AVX512_VBMI
dts                               DS
pni                               SSE3
tsc_deadline_timer                TSC_DEADLINE