Pull in r223147, r223255 and r223390 from upstream llvm trunk (by Roman
Divacky):

  Introduce CPUStringIsValid() into MCSubtargetInfo and use it for ARM
  .cpu parsing.

  Previously .cpu directive in ARM assembler didnt switch to the new
  CPU and therefore acted as a nop. This implemented real action for
  .cpu and eg. allows to assembler FreeBSD kernel with -integrated-as.

  Change the name to be in style.

  Add a FIXME as requested by Renato Golin.
Add llvm patch corresponding to r275654, and clean up a few other patches.