Currently supports initialization, read, write, and erase operations.
Tested on HiFive Uneashed
implementation follows SD association's SPI access protocol, found
as doc http://t.cn/AiB8quFZ
Change-Id: I464d2334b8227e448c1c7e324c0455023cffb72a
Signed-off-by: Xiang Wang <merle@hardenedlinux.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35118
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
