It makes more sense to set the optimization flags on a platform basis
instead of individually for each module. This allows for different
optimization options for SITL, NuttX, Snapdragon, etc.
The name uart_esc was initially taken by Qualcomm's UART ESC driver but
then got changed into the current mavlink ESC/RC helper. Since the
uart_esc is still around, we should prevent the names clashing.