[RS6000] CONST_DOUBLE tidy

[RS6000] CONST_DOUBLE tidy

Once upon a time CONST_DOUBLE was used to hold large integer constants
that didn't fit into a CONST_INT.  Now that CONST_INT is always at
least 64 bits, and the rs6000 backend uses CONST_WIDE_INT for larger
integers, there is no need for old code dealing with integers in
CONST_DOUBLE.  The rs6000 backend also doesn't create DImode subregs
of TFmode CONST_DOUBLE, as once we did.  This patch cleans up a few
leftovers from the past.

	* config/rs6000/predicates.md (easy_fp_constant): Remove code
	dealing with integers in const_double.  Assert on unexpected
	modes.  Delete superfluous ABI_V4 test.
	* config/rs6000/rs6000.c (rs6000_emit_move): Comment fixes.
	Don't call easy_fp_constant for Pmode.
	(rs6000_hash_constant): Remove code dealing with integers in
	const_double.
	(rs6000_legitimate_constant_p): Likewise.
	(output_toc): Formatting, use CONST_DOUBLE_P.

From-SVN: r266608