PPC: Add new relocation type WASM_MEMORY_SIZE_REFERENCE, use relocatable pointers to update wasm memory size references in generated code.

Port 117a56b7

Original commit message:

     - Add new RelocInfo mode WASM_MEMORY_SIZE_REFERENCE in the assembler and add relocation information to immediates in compare instructions.
     - Use relocatable constants for MemSize/BoundsCheck in the wasm compiler

R=gdeepti@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=
LOG=N

Review-Url: https://codereview.chromium.org/1948263003
Cr-Commit-Position: refs/heads/master@{#36054}