r600: add missing <array> include

Fixes error with clang/libc++:

../src/gallium/drivers/r600/sfn/sfn_emitaluinstruction.h:69:88: error: implicit instantiation of undefined template 'std::__1::array<unsigned char, 3>'
   bool emit_alu_op3(const nir_alu_instr& instr, EAluOp opcode, std::array<uint8_t, 3> reorder={0,1,2});