Speedup - loadMatrixBuffers

Zero all the pad and clk bits in parallel (rather than doing it bit by bit)

Use 2 MOVS instructions instead of 8 BFC instructions
Inside loop, so saves 192 instructions per row
(at 16 rows for a 32x32 panel, and 120 refresh per second this saves about 368,000 instructions per second)
should mean less overhead doing refreshes