spi: make falcon-spi bool

Falcon spi accesses some ebu functions which are not exported and can
not be accessed when build as module. Make this module bool instead.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Thomas Langer <thomas.langer@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>