On a second look broadcom/cygnus and imgtec/pistachio appear to
support full duplex. Therefore, remove the use of spi_xfer_two_vectors().
For mediatek/mt8173 and qualcomm/ipq40xx, the driver is written in such
a way that it does not support full duplex. Remove the use of
spi_xfer_two_vectors() and explicitly error out when a full duplex
transaction is requested.
Change-Id: I8689bc9bb2b27563d25e9f165487d38881c0b059
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/25742
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
9a1bb36137