Adjust PPC A2 input operand latencies

On the PPC A2, instructions are only issued after their input operands are
ready. Model this by specifying that input operands are read at dispatch (0
cycles after issue). This changes all input operand latencies from 1 to 0.

Significant test-suite performance changes (these are 99.5% confidence
intervals on 6 runs for both before and after):

speedups:
MultiSource/Benchmarks/sim/sim
	-1.21915% +/- 0.175063%
MultiSource/Benchmarks/TSVC/LinearDependence-flt/LinearDependence-flt
	-1.23946% +/- 1.05133%
SingleSource/Benchmarks/Misc/flops-2
	-1.24237% +/- 0.681362%
MultiSource/Applications/JM/lencod/lencod
	-1.33992% +/- 0.757498%
MultiSource/Benchmarks/TSVC/InductionVariable-flt/InductionVariable-flt
	-1.51802% +/- 1.21468%
MultiSource/Benchmarks/TSVC/GlobalDataFlow-flt/GlobalDataFlow-flt
	-2.18818% +/- 1.28605%
MultiSource/Benchmarks/TSVC/Packing-flt/Packing-flt
	-2.21977% +/- 1.19499%
SingleSource/Benchmarks/BenchmarkGame/spectral-norm
	-2.29822% +/- 0.671871%
MultiSource/Benchmarks/TSVC/Packing-dbl/Packing-dbl
	-2.40975% +/- 0.355931%
SingleSource/Benchmarks/Misc/fp-convert
	-2.41899% +/- 1.04751%
MultiSource/Benchmarks/TSVC/Searching-dbl/Searching-dbl
	-2.50349% +/- 0.126765%
SingleSource/Benchmarks/Misc/flops-3
	-3.00214% +/- 0.700795%
MultiSource/Benchmarks/TSVC/LoopRestructuring-flt/LoopRestructuring-flt
	-3.56995% +/- 3.2929%
MultiSource/Applications/sgefa/sgefa
	-4.24908% +/- 2.00413%
MultiSource/Benchmarks/ASC_Sequoia/IRSmk/IRSmk
	-18.1294% +/- 3.96489%

regressions:
MultiSource/Benchmarks/TSVC/Reductions-dbl/Reductions-dbl
	1.03249% +/- 0.178547%
MultiSource/Applications/hexxagon/hexxagon
	1.16597% +/- 0.285235%
MultiSource/Benchmarks/TSVC/IndirectAddressing-flt/IndirectAddressing-flt
	1.39576% +/- 1.07855%
SingleSource/Benchmarks/Misc-C++/stepanov_v1p2
	1.71539% +/- 0.173182%
MultiSource/Benchmarks/Fhourstones-3.1/fhourstones3.1
	1.90013% +/- 0.866472%
MultiSource/Benchmarks/TSVC/Recurrences-dbl/Recurrences-dbl
	2.39854% +/- 1.05914%
MultiSource/Benchmarks/TSVC/ControlFlow-dbl/ControlFlow-dbl
	2.4402% +/- 0.817904%
MultiSource/Benchmarks/TSVC/LoopRestructuring-dbl/LoopRestructuring-dbl
	5.87997% +/- 3.3172%
MultiSource/Benchmarks/Trimaran/netbench-crc/netbench-crc
	9.02643% +/- 5.79591%
MultiSource/Benchmarks/VersaBench/bmm/bmm
	10.3517% +/- 1.227%

Obviously, there are data points on both sides of this; but I think, overall,
this supports making the change.