RFR: 8344074: RISC-V: More accurate _exception_handler_size and _deopt_handler_size

[Fei Yang]

Hi, please review this small change.

I find that the reserved size for these two handlers are not accurate and are larger than needed.
For _exception_handler_size, the used size is only 20 bytes for release build and about 60 bytes
for debug build. Considering that exception_handler is not trivial, I reserved a little bit more
than needed for release build. For _deopt_handler_size, `far_jump` will always emit two instructions.

Testing on linux-riscv64:
- [x] tier1 (release)
- [x] hotspot:tier1 (fastdebug)

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Commit messages:
 - 8344074: RISC-V: More accurate _exception_handler_size and _deopt_handler_size

Changes: https://git.openjdk.org/jdk/pull/22053/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22053&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344074
  Stats: 4 lines in 1 file changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/22053.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22053/head:pull/22053

PR: https://git.openjdk.org/jdk/pull/22053