[Mips] Do not use llvm::Optional for GP0 value and TLS section address
[Mips] Do not use llvm::Optional for GP0 value and TLS section address

Use of llvm::Optional is redundant here. Initializing by default value 0
is enough.

No functional changes.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@233549 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld