linux_spi: Dynamically detect max buffer size

Read max buffer size from sysfs if available.

Change-Id: Ic541e548ced8488f074d388f1c92174cad123064
Signed-off-by: Keno Fischer <keno@juliacomputing.com>
Signed-off-by: David Hendricks <dhendricks@fb.com>
Reviewed-on: https://review.coreboot.org/22441
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
1 file changed