[mips] Fix sc, scs, ll, lld instructions expanding

[mips] Fix sc, scs, ll, lld instructions expanding

There are a couple of bugs with the sc, scs, ll, lld instructions expanding:

1. On R6 these instruction pack immediate offset into a 9-bit field. Now
if an immediate exceeds 9-bits assembler does not perform expansion and
just rejects such instruction.

2. On 64-bit non-PIC code if an operand is a symbol assembler generates
incorrect sequence of instructions. It uses R_MIPS_HI16 and R_MIPS_LO16
relocations and skips R_MIPS_HIGHEST and R_MIPS_HIGHER ones.

To solve these problems this patch:
- Introduces `mem_simm9_exp` to mark 9-bit memory immediate operands
which require expansion. Probably later all `mem_simm9` operands will be
able to migrate on `mem_simm9_exp` and we rename it to `mem_simm9`.

- Adds new `OPERAND_MEM_SIMM9` operand type and assigns it to the
`mem_simm9_exp`. That allows to know operand size in the `processInstruction`
method and decide whether we need to expand instruction.

- Adds `expandMem9Inst` method to expand instructions with 9-bit memory
immediate operand. This method just load immediate into a "base"
register used by origibal instruction:

   sc $2, 256($sp) => addiu  $1, $sp, 256
                      sc     $2, 0($1)

- Fix `expandMem16Inst` to support a correct set of relocations for
symbol loading in case of 64-bit non-PIC code.

   ll $12, symbol => lui    $12, 0
                         R_MIPS_HIGHEST symbol
                     daddiu $12, $12, 0
                         R_MIPS_HIGHER symbol
                     dsll   $12, $12, 16
                     daddiu $12, $12, 0
                         R_MIPS_HI16 symbol
                     dsll   $12, $12, 16
                     ll     $12, 0($12)
                         R_MIPS_LO16 symbol

- Fix `expandMem16Inst` to unify handling of 3 and 4 operands
instructions.

- Delete unused now `MipsTargetStreamer::emitSCWithSymOffset` method.

Task for next patches - implement expanding for other instructions use
`mem_simm9` operand and other `mem_simm##` operands.

Differential Revision: https://reviews.llvm.org/D70648