Fix issues with Arm's use of embedded constant pools

Fix issues with Arm's use of embedded constant pools

- Introduce Assembler::DataAlign for table alignment in code object
- Fix several misuses of r8 (alias of the pool pointer register, pp)
- Fix calculation of pp in OSR/handler entry invocation
- Enable missing cases in deserializer
- Fix references to ool constant pools in comments.

R=rmcilroy@chromium.org, michael_dawson@ca.ibm.com
BUG=chromium:497180
LOG=N

Review URL: https://codereview.chromium.org/1155673005

Cr-Commit-Position: refs/heads/master@{#28873}