RFR: 8260716 : Assert in MacroAssembler::clear_mem with -XX:-IdealizeClearArrayNode

[Jamsheed Mohammed C M]

[8257772](https://bugs.openjdk.java.net/browse/JDK-8257772) added a new rule(rep_stos_im), modified old rules(rep_stos) missed adding proper predicates relating to UseAVX and supports_avx512vlbw

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Commit messages:
 - Added proper predicates to guard newly added rules
 - Merge branch 'master' of https://github.com/jamsheedcm/jdk
 - Merge pull request #3 from openjdk/master
 - Merge branch 'master' of https://github.com/jamsheedcm/jdk
 - Merge pull request #2 from openjdk/master
 - Merge branch 'master' of https://github.com/jamsheedcm/jdk
 - Merge pull request #1 from openjdk/master

Changes: https://git.openjdk.java.net/jdk/pull/3035/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3035&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260716
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3035.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3035/head:pull/3035

PR: https://git.openjdk.java.net/jdk/pull/3035