Check the HTT bit before counting logical threads

Skip counting logical threads for Intel processors if the HTT bit is 0
which indicates there is only a single logical processor.

	* sysdeps/x86/cacheinfo.c (init_cacheinfo): Skip counting
	logical threads if the HTT bit is 0.
	* sysdeps/x86/cpu-features.h (bit_cpu_HTT): New.
	(index_cpu_HTT): Likewise.
	(reg_HTT): Likewise.