Enable MOVDIRI, MOVDIR64B, CLDEMOTE and WAITPKG for march=tremont

1. Enable MOVDIRI, MOVDIR64B, CLDEMOTE and WAITPKG for march=tremont
2. Move PREFETCHW from march=broadwell to march=silvermont.
3. Add PREFETCHWT1 to march=knl

gcc/ChangeLog:

2020-11-09  Lili Cui  <lili.cui@intel.com>

	PR target/97685
	* config/i386/i386.h:
	(PTA_BROADWELL): Delete PTA_PRFCHW.
	(PTA_SILVERMONT): Add PTA_PRFCHW.
	(PTA_KNL): Add PTA_PREFETCHWT1.
	(PTA_TREMONT): Add PTA_MOVDIRI, PTA_MOVDIR64B, PTA_CLDEMOTE and PTA_WAITPKG.
	* doc/invoke.texi: Delete PREFETCHW for broadwell, skylake, knl, knm,
	skylake-avx512, cannonlake, icelake-client, icelake-server, cascadelake,
	cooperlake, tigerlake and sapphirerapids.
	Add PREFETCHW for silvermont, goldmont, goldmont-plus and tremont.
	Add XSAVEC and XSAVES for goldmont, goldmont-plus and tremont.
	Add MOVDIRI, MOVDIR64B, CLDEMOTE and WAITPKG for tremont.
	Add KEYLOCKER and HREST for alderlake.
	Add AMX-BF16, AMX-TILE, AMX-INT8 and UINTR for sapphirerapids.
	Add KEYLOCKER for tigerlake.