RFR: 8355980: RISC-V: remove vmclr_m before vmsXX and vmfXX

[Hamlin Li]

Hi,
Can you help to review this simple improvement?

By rvv spec,
"integer compare instructions write 1 to the destination mask register element if the comparison evaluates to true, and 0 otherwise."
"These vector FP compare instructions compare two source operands and write the comparison result to a mask register. "

So, it's not always necessary to clear the mask register before vector comparison operation, e.g. when `vm != Assembler::v0_t`.

Thanks!

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Commit messages:
 - fix
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/24968/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24968&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355980
  Stats: 6 lines in 1 file changed: 4 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/24968.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24968/head:pull/24968

PR: https://git.openjdk.org/jdk/pull/24968