[AArch64][SVE] Allow vector of pointers as legal type for masked load/store.

Refer to LangRef http://llvm.org/docs/LangRef.html#llvm-masked-load-intrinsics
'llvm.masked.load/store.*’ intrinsics are overloaded intrinsic, which allow the
load/store data to be a vector of any integer, floating-point or pointer data type.

Therefore, allow pointer data type when checking 'isLegalMaskedLoadStore()'.

Reviewed By: paulwalker-arm

Differential Revision: https://reviews.llvm.org/D85045