RFR: 8285802: AArch64: Consistently handle offsets in MacroAssembler as 64-bit quantities

[Andrew Haley]

In a few places we pass offsets as 32-bit ints rather than 64-bit longs, and we're not consistent about it. We shold have a clean 64-bit path for offset generation and validation.

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Commit messages:
 - 8285802: AArch64: Consistently handle offsets in MacroAssembler as 64-bit quantities

Changes: https://git.openjdk.java.net/jdk/pull/8448/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8448&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285802
  Stats: 11 lines in 2 files changed: 0 ins; 0 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8448.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8448/head:pull/8448

PR: https://git.openjdk.java.net/jdk/pull/8448