[X86][X87]: Adding full coverage of MC encoding for all X87 ISA Sets.<NFC>

NFC.
 Currently, not all the X86 ISA Sets are covered by the MC regressions tests for X86.
 A full coverage needs to be added for each ISA set and for both 32bit and 64bit instructions + registers.
 This patch includes MC assembly tests for the X87 32bit and 64bit.

Reviewers: craigt, RKSimon, zvi
Differential Revision: https://reviews.llvm.org/D39952

Change-Id: I55e1719c09a70644a6a4073c720cb5341c80fee9

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320015 91177308-0d34-0410-b5e6-96231b3b80d8