[code-reflection] Integrated: We should be able to select platform/device via env var

[Gary Frost]

We can request specific opencl platform and device

Default is platfom:0 device:0

We can pass via HAT env var

HAT=PLATFORM:0,DEVICE:0 java @bldr/hatrun ffi-opencl life

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

Commit messages:
 - We should be able to select platform/device via env var

Changes: https://git.openjdk.org/babylon/pull/355/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=355&range=00
  Stats: 638 lines in 9 files changed: 227 ins; 373 del; 38 mod
  Patch: https://git.openjdk.org/babylon/pull/355.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/355/head:pull/355

PR: https://git.openjdk.org/babylon/pull/355