spi: Reorder functions to simplify the next commit

Currently the "Core methods for SPI resource management" are exported
and public functions. They are however only used in drivers/spi/spi.c.
To allow to drop the global declarations and not to have to insert local
ones instead, move them before their users.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211007121415.2401638-4-u.kleine-koenig@pengutronix.de


Signed-off-by: Mark Brown <broonie@kernel.org>