RFR: 8295016: Make the arraycopy_epilogue signature consistent with its usage

[Zixian Cai]

The second register argument should be named `count`. Please see the following usage.

https://github.com/openjdk/jdk/blob/495c043533d68106e07721b2e971006e9eba97e3/src/hotspot/cpu/riscv/stubGenerator_riscv.cpp#L1138

https://github.com/openjdk/jdk/blob/495c043533d68106e07721b2e971006e9eba97e3/src/hotspot/cpu/riscv/stubGenerator_riscv.cpp#L1210

https://github.com/openjdk/jdk/blob/495c043533d68106e07721b2e971006e9eba97e3/src/hotspot/cpu/riscv/stubGenerator_riscv.cpp#L1584

Update: also fix for AArch64.

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Commit messages:
 - AArch64: Make the arraycopy_epilogue signature consistent with its usage
 - RISC-V: Make the arraycopy_epilogue signature consistent with its usage

Changes: https://git.openjdk.org/jdk/pull/10620/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10620&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295016
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/10620.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10620/head:pull/10620

PR: https://git.openjdk.org/jdk/pull/10620