Test for YMMRegisters.

Summary:
This patch contains test for reading YMM Registers. The test basically
contains an inferior that loads the ymm registers with a bit pattern
and the python test executes register read to check if the bit pattern
is correctly written in the registers. This test is repeated twice for
each register with a different pattern for better sanity.

Reviewers: tberghammer, zturner, clayborg

Subscribers: tberghammer, danalbert, srhines

Differential Revision: https://reviews.llvm.org/D26242

llvm-svn: 285885