qualcomm/ipq40xx: add vector operation method to SPI

Adding spi_xfer_two_vectors as .xfer_vector for ipq40xx spi_ctrlr.
Commit c2973d196d ("UPSTREAM: spi: Get rid of SPI_ATOMIC_SEQUENCING")
has added a new driver method xfer_vector to support combined write-read
operation within a single CS cycle. The method is wrapped in the
spi_xfer_vector() API. When spi_ctrlr structure does not have
xfer_vector method, API calls write and read operations sequentially.
However the QCA40xx SPI driver has "forced" CS activation-inactivation
in xfer method, so individual operation will break CS after write
operation, making combined write-read cycle broken.
Adding xfer_vector method to spi_ctrlr is a simple fix to prevent this.

BUG=None
BRANCH=none
TEST=built and run on Gale

Change-Id: I2258e563d0793bcacd626f78b8e96b3649a8e4a4
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 88a8824951cef4fe293dfa6e3a1a837ae07b6156
Original-Change-Id: I031e85ce5b847353cb1084f6f68b2af8c6f702e1
Original-Signed-off-by: Yuji Sasaki <sasakiy@google.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/433439
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-by: Kan Yan <kyan@google.com>
Reviewed-on: https://review.coreboot.org/18297
Tested-by: build bot (Jenkins)
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/qualcomm/ipq40xx/spi.c

@@ -656,6 +656,7 @@ static const struct spi_ctrlr spi_ctrlr = {
 	.claim_bus = spi_ctrlr_claim_bus,
 	.release_bus = spi_ctrlr_release_bus,
 	.xfer = spi_ctrlr_xfer,
+	.xfer_vector = spi_xfer_two_vectors,
 };
 
 int spi_setup_slave(unsigned int bus, unsigned int cs, struct spi_slave *slave)