rs6000: Disable HTM for Power10 and later by default

rs6000: Disable HTM for Power10 and later by default

Power ISA 3.1 has dropped transactional memory support, this patch
is to disable HTM feature for power10 and later by default.

Bootstrapped/regtested on powerpc64le-linux-gnu P8 and P10.

gcc/ChangeLog:

	* config/rs6000/rs6000.c (rs6000_option_override_internal):
	Use OPTION_MASK_DIRECT_MOVE for Power8 target_enable instead
	of OPTION_MASK_HTM.
	* config/rs6000/rs6000-cpus.def (ISA_2_7_MASKS_SERVER):
	Remove OPTION_MASK_HTM.
	(RS6000_CPU): Add OPTION_MASK_HTM to power8, power9 and
	powerpc64le entries.