[RISCV] Expand function call to "call" pseudoinstruction

To do this:
1. Change GlobalAddress SDNode to TargetGlobalAddress to avoid legalizer
   split the symbol.

2. Change ExternalSymbol SDNode to TargetExternalSymbol to avoid legalizer
   split the symbol.

3. Let PseudoCALL match direct call with target operand TargetGlobalAddress
   and TargetExternalSymbol.

Differential Revision: https://reviews.llvm.org/D44885

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330827 91177308-0d34-0410-b5e6-96231b3b80d8
26 files changed