Improved efficiency of SPI drivers

_examples/display_er_oledm015/main.cpp

_examples/display_er_oledm024/display_er_oledm024.cpp

_examples/display_er_oledm024/main.cpp

_examples/display_er_oledm028/display_er_oledm028.cpp

_examples/display_er_oledm028/main.cpp