Fix movelh-ps and movehl-ps intrinsics

- movlhps and movhlps instructions only work with registers. To support operands
in memory, need to generate movhps and movlps. They have the same opcodes, but
different assertions in SBCL's assembler.

- Modify def-binary-intrinsic to accept a keyword parameter :mem-alt-insn to
specify the instruction to use if the src operand is in memory.