RFR: 8286056: AArch64: clarify uses of MacroAssembler::far_call/MacroAssembler::far_jump [v2]

[Evgeny Astigeevich]

> `MacroAssembler::far_call`/`MacroAssembler::far_jump` are for generating calls of/jumps to targets which are inside `CodeCache` and can `relocInfo` types: `external_word_type`, `runtime_call_type` or `none`.
> This PR updates the description of the functions and adds an assert checking a `relocInfo` type.
> Tested a fastdebug build:
> - `gtest`: Passed
> - `tier1`: Passed

Evgeny Astigeevich has updated the pull request incrementally with one additional commit since the last revision:

  Add additional comments to far_call/far_branch

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8534/files
  - new: https://git.openjdk.java.net/jdk/pull/8534/files/9e6e89df..fd5689bb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8534&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8534&range=00-01

  Stats: 7 lines in 1 file changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8534.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8534/head:pull/8534

PR: https://git.openjdk.java.net/jdk/pull/8534