vertexjit: Use SSE4.1 where available on x86.

Just because we can.
vertexjit: Add VQMOV(U)N and fix VMOVN size.

It will be too confusing if it's specified as the destination, unlike
VMOVL.  Plus the assembler syntax uses the source size.
vertexjit: support 8888 morph on ARM.
Fix VMOV for Dregs and VSHL reg order.
vertexjit: Attempt 16-bit color morphs on ARM.
vertexjit: Save S16-S31 registers in ARM.
Fix VLD1/VST1 n=4.
vertexjit: Implement NEON color morphs on ARM.
vertexjit: Improve NEON align on color morph ARM.