RFR: 8293942: [JVMCI] data section entries must be 4-byte aligned on AArch64

[Doug Simon]

As a result of [JDK-8283626](https://bugs.openjdk.org/browse/JDK-8283626), each entry in a data section in a CodeBuffer on AArch64 needs to be 4-byte aligned. This PR exposes this alignment requirement via JVMCI so that Graal can adhere to it.

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Commit messages:
 - expose min alignment for data section items via JVMCI

Changes: https://git.openjdk.org/jdk/pull/10308/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10308&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293942
  Stats: 16 lines in 4 files changed: 16 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10308.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10308/head:pull/10308

PR: https://git.openjdk.org/jdk/pull/10308