We should use pc relative branch instruction rather than loading
target address from memory for better performance.

Besides, just like arm64, currently we assume that none of our
relocation types are pc relative pointing outside the code buffer
nor pc absolute pointing inside the code buffer.

Change-Id: I9cce2e79c0afb00af967638405469f65df1deda2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3147314Reviewed-by: Liu yu <liuyu@loongson.cn>
Commit-Queue: Liu yu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/main@{#76721}