nouveau: codegen: LOAD: Take src swizzle into account

The llvm TGSI backend uses pointers in registers and does things
like:

LOAD TEMP[0].y, MEMORY[0], TEMP[0]

Expecting the data at address TEMP[0].x to get loaded to
TEMP[0].y. But this will cause the data at TEMP[0].x + 4 to be
loaded instead.

This commit adds support for a swizzle suffix for the 1st source
operand, which allows using:

LOAD TEMP[0].y, MEMORY[0].xxxx, TEMP[0]

And actually getting the desired behavior

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>

src/gallium/docs/source/tgsi.rst

@@ -2288,6 +2288,9 @@ Resource Access Opcodes
                texture arrays and 2D textures.  address.w is always
                ignored.
 
+               A swizzle suffix may be added to the resource argument
+               this will cause the resource data to be swizzled accordingly.
+
 .. opcode:: STORE - Write data to a shader resource
 
                Syntax: ``STORE resource, address, src``