[riscv-port-jdk11u:riscv-port] RFR: 8293524: RISC-V: Use macro-assembler functions as appropriate

[Dingli Zhang]

Please review this backport to riscv-port-jdk11u.
Backport of [JDK-8293524](https://bugs.openjdk.org/browse/JDK-8293524).
The original patch cannot be directly applied because jdk11u has no [JDK-8241436 ](https://bugs.openjdk.org/browse/JDK-8241436 ) and [JDK-8229258](https://bugs.openjdk.org/browse/JDK-8229258) . Also jdk11u does not have generate_bigIntegerLeftShift and generate_bigIntegerRightShift functions.

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Commit messages:
 - 8293524: RISC-V: Use macro-assembler functions as appropriate

Changes: https://git.openjdk.org/riscv-port-jdk11u/pull/34/files
  Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk11u&pr=34&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293524
  Stats: 76 lines in 12 files changed: 0 ins; 0 del; 76 mod
  Patch: https://git.openjdk.org/riscv-port-jdk11u/pull/34.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk11u.git pull/34/head:pull/34

PR: https://git.openjdk.org/riscv-port-jdk11u/pull/34