It is not necessary to hold a complete copy `sdcard_spi_params_t` in the device descriptor. Constant parameters can be used directly from ROM instead. This saves 24 bytes of RAM.
- replace all `int`s and `unsigned`s with integers with fixed width
- replaced all signed integers of sizes with unsigned ones (sizes
cannot be negative)
- made bitshifts 8-bit safe (e.g. `1 << 24` is valid on 32-bit, but
undefined behavior on 8-bit, as a 16 bit wide `int` would be shifted
by more than the type width)
- use `void *` / `const void *` for data buffers to ease use
