VideoCommon:VertexLoaderManager: Reduce CPConfig checks

[K0bin]

A bit of a micro optimization:
With this PR CheckCPConfiguration runs 350 times instead of 35k times. (Mario Galaxy)

[Pokechu22]

Untested, looks good to me though

[Pokechu22]

This check can probably be removed entirely, actually, as it's redundant with this:

dolphin/Source/Core/VideoCommon/OpcodeDecoding.h

Lines 234 to 240 in c8705f0

	const u32 vertex_size = callback.GetVertexSize(vat);
	const u16 num_vertices = Common::swap16(&data[1]);
	if (available < 3 + num_vertices * vertex_size)
	return 0;
	callback.OnPrimitiveCommand(primitive, vat, vertex_size, num_vertices, &data[3]);

and in fact this return value isn't properly handled anymore:

dolphin/Source/Core/VideoCommon/OpcodeDecoding.cpp

Lines 122 to 127 in c8705f0

	// HACK
	DataReader src{const_cast<u8*>(vertex_data), const_cast<u8*>(vertex_data) + size};
	const u32 bytes =
	VertexLoaderManager::RunVertices<is_preprocess>(vat, primitive, num_vertices, src);
	ASSERT(bytes == size);

It doesn't need to be removed in this PR, but this is probably something that can be refactored later (along with the DataReader itself since it isn't really doing much anymore to my understanding).

[K0bin]

I think I'll leave that to you since you understand that code muuuuch better than me. ;)