RFR: 8300253: Introduce AArch64 nzcv accessors

[Hao Sun]

On Wed, 18 Jan 2023 10:32:33 GMT, Stuart Monteith <smonteith at openjdk.org> wrote:

>> OK, I'm not wild about checking in dead code, but if it's imminently needed, OK. Please add the instructions to  `test/hotspot/gtest/aarch64/aarch64-asmtest.py` so they get tested..
>
> The bits for the instructions are correct. I presume there'll be a train of patches for ZGC generational to necessitate it.

I suggest adding one comment here. How about:

// macro instructions for accessing and updating 
// PSTATE.{N,Z,C,V} fields at EL0
//
// NZCV:  op1 = 011
//        CRn = 0100
//        CRm = 0010
//        op2 = 000

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PR: https://git.openjdk.org/jdk/pull/12038