[ELF] - X86_64: Use white list for relocations checked by isPicRel.

isPicRel is used to check if we want to create the dynamic relocations.
Not all of the dynamic relocations we create are passing through this
check, but those that are, probably better be whitelisted.

Differential revision: https://reviews.llvm.org/D45252

llvm-svn: 329203