r300: Cleaned up vertprog construction.

r300: Cleaned up vertprog construction.

Construct the vertprog instruction in the 4 DWORD parts...

DWORD 0: Opcode and Output.
DWORD 1: First Argument.
DWORD 2: Second Argument.
DWORD 3: Third Argument.

Allow the opcode translation functions to generate more than one instruction;
useful for when an instruction must be emulated. FLR, XPD, etc.