[RISCV] Add assembler support for LA pseudo-instruction

This patch also introduces the emitAuipcInstPair helper, which is then used
for both emitLoadAddress and emitLoadLocalAddress.

Differential Revision: https://reviews.llvm.org/D55325
Patch by James Clarke.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354111 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed