bpf: set missing types in insn tablegen file

o This is discovered during my study of 32-bit subregister
  support.
o This is no impact on current functionality since we
  only support 64-bit registers.
o Searching the web, looks like the issue has been discovered
  before, so fix it now.

Signed-off-by: Yonghong Song <yhs@fb.com>
llvm-svn: 305559