[15] RFR (M): 8238680: C2: Remove redundant AD instructions for Replicate nodes

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8238680/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8238680

Replicate nodes have special handling on x86 for 512-bit case when 
AVX-512VL is absent.

But according to Software Developer’s Manual from Intel, EVEX-encoded 
VPBROADCASTD/VPBROADCASTQ/VBROADCASTSS/VBROADCASTSD only require AVX512F 
for full 512-bit registers (VL is needed for 128-/256-bit cases), so no 
special handling is needed.

The patch removes redundant AD instructions (Repl[ILFD]_[reg|mem]_leg) 
and adjusts generic instructions to handle all cases uniformly.

Testing: tier1-4

Thanks!

Best regards,
Vladimir Ivanov