RFR (S) 8131682: C1 should use multibyte nops everywhere

[Aleksey Shipilev]

Hi there,

C1 is not very good at inlining and intrisifying methods, and hence the
call performance is important there. One nit that we can see in the
generated code on x86 is that C1 uses the single-byte nops, even for
long nop strides.

This improvement fixes that:
  https://bugs.openjdk.java.net/browse/JDK-8131682
  http://cr.openjdk.java.net/~shade/8131682/webrev.00/

Testing:
  - JPRT -testset hotspot on open platforms
  - eyeballing the generated assembly with -XX:TieredStopAtLevel=1

(I understand the symmetric change is going to be needed in closed
parts, but let's polish the open part first).

Thanks,
-Aleksey

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