Fix .cfi_restore with register numbers > 64

Summary:
DW_CFA_restore can only encode register numbers up to 64 (6 bits unsigned
int). For regsiter numbers > 64 we have to use DW_CFA_restore_extended
instead which uses a ULEB128 value.
I discovered this problem in the out-of-tree CHERI target since we use
DWARF register number 89 for our return capability register.

Reviewers: probinson, dblaikie, aprantl, espindola

Reviewed By: dblaikie

Subscribers: JohnReagan, emaste, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D54420

llvm-svn: 346751