soc/sifive/fu540: test and fix code of fu540 spi

I tested the SPI through the SD card and fixed sd card communication problem.
Added two functions (claim_bus and release_bus). Setting CS signal is invalid by
default.

Change-Id: I60033a148c21bbd5b4946580f6cab0b439d346c6
Signed-off-by: Xiang Wang <merle@hardenedlinux.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35117
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

0 files changed, 0 insertions, 0 deletions