Calls to Spi::Init() are not needed, pin initialization is already done in ctor().
Remove calls to Spi::Sleep()/Spi::Wakeup() to ensure that SPI CS pins are kept high even in sleep mode.
Ensure that all pins are set to their default configuration during sleep mode.
Disable the workaround for FTPAN58 (SPI freezes when transfering a single byte) at the end of the transfer. This disables the resources needed for the workaround.
Those changes reduce the power usage by 430-490µA.
Don't use relative imports like `../foo.h` as those depend on the
relative position of both files. Rather than that use imports relative
to the `src` directory, which explicitly is part of the include
directories.
