RFR: 8333382: [s390x] Enhance popcnt Instruction to use Z15 facilities [v8]

[Amit Kumar]

> We need to move popcnt instruction implementation out of s390.ad file as it is required to be required some methods present in [JDK-8331126.](https://bugs.openjdk.org/browse/JDK-8331126)
> 
> 
> When the miscellaneous-instruction-extensions facility 3 is not installed or bit 0 of the M3
>  field is zero, a count of the number of one bits in each of the eight bytes of general register
>  R2 is placed into the corresponding byte of general register R1. Each byte of general register 
> R1 is an 8-bit binary integer in the range of 0-8.
> 
> 
> 
> When the miscellaneous-instruction-extensions facility 3 is installed and bit 0 of the M3 field
> is one, a count of the total number of one bits in the 64-bit general register R2 is placed into 
> general register R1. The result is a 64-bit unsigned integer in the range 0 to 64.
> 
> 
> Performed tier1 test on fastdebug build and didn't see any regression.

Amit Kumar has updated the pull request incrementally with one additional commit since the last revision:

  removes if and uses guarantee

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/19509/files
  - new: https://git.openjdk.org/jdk/pull/19509/files/ebca276e..712b9b45

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19509&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19509&range=06-07

  Stats: 11 lines in 1 file changed: 0 ins; 4 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/19509.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19509/head:pull/19509

PR: https://git.openjdk.org/jdk/pull/19509