drivers/spi/spi_flash: don't allocate unbounded stack memory

This open-codes flash_cmd, but until the API is fixed for real, it uses
xfer's existing scatter-gather ability to write command and data in one
go.

BUG=chromium:446201
TEST=emerge-coral coreboot succeeds

Change-Id: Ic81b7c9f7e0f2647e59b81d61abd68d36051e578
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/28254
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
1 file changed