Allow {e,r}bp as the target of {read,write}_register.

Allow {e,r}bp as the target of {read,write}_register.

This patch allows the read_register and write_register intrinsics to
read/write the RBP/EBP registers on X86 iff the targeted register is
the frame pointer for the containing function.

Differential Revision: http://reviews.llvm.org/D10977

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241827 91177308-0d34-0410-b5e6-96231b3b80d8