PPC: Switch CallConstructStub to take new.target in register.

PPC: Switch CallConstructStub to take new.target in register.

Port 1d9d895754e1d1cf824c11a9cce5e495fa47d5e2

Original commit message:
    This changes the calling convention of the CallConstructStub to take
    the original constructor (i.e. new.target in JS-speak) in a register
    instead of magically via the operand stack. For optimizing compilers
    the operand stack doesn't exist, hence cannot be peeked into.

R=mstarzinger@chromium.org, dstence@us.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1230103004

Cr-Commit-Position: refs/heads/master@{#29702}