spi: Define and use spi_ctrlr structure

1. Define a new structure spi_ctrlr that allows platforms to define
callbacks for spi operations (claim bus, release bus, transfer).
2. Add a new member (pointer to spi_ctrlr structure) in spi_slave
structure which will be initialized by call to spi_setup_slave.
3. Define spi_claim_bus, spi_release_bus and spi_xfer in spi-generic.c
which will make appropriate calls to ctrlr functions.

BUG=chrome-os-partner:59832
BRANCH=None
TEST=Compiles successfully

Change-Id: Icb2326e3aab1e8f4bef53f553f82b3836358c55e
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/17684
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/southbridge/amd/agesa/hudson/spi.c b/src/southbridge/amd/agesa/hudson/spi.c
index a8b3b2a..8a4adfb 100644
--- a/src/southbridge/amd/agesa/hudson/spi.c
+++ b/src/southbridge/amd/agesa/hudson/spi.c
@@ -90,7 +90,7 @@
 	return min(AMD_SB_SPI_TX_LEN - cmd_len, buf_len);
 }
 
-int spi_xfer(const struct spi_slave *slave, const void *dout,
+static int spi_ctrlr_xfer(const struct spi_slave *slave, const void *dout,
 		size_t bytesout, void *din, size_t bytesin)
 {
 	/* First byte is cmd which can not being sent through FIFO. */
@@ -147,17 +147,6 @@
 	return 0;
 }
 
-int spi_claim_bus(const struct spi_slave *slave)
-{
-	/* Nothing is required. */
-	return 0;
-}
-
-void spi_release_bus(const struct spi_slave *slave)
-{
-	/* Nothing is required. */
-}
-
 int chipset_volatile_group_begin(const struct spi_flash *flash)
 {
 	if (!IS_ENABLED (CONFIG_HUDSON_IMC_FWM))
@@ -176,9 +165,14 @@
 	return 0;
 }
 
+static const struct spi_ctrlr spi_ctrlr = {
+	.xfer = spi_ctrlr_xfer,
+};
+
 int spi_setup_slave(unsigned int bus, unsigned int cs, struct spi_slave *slave)
 {
 	slave->bus = bus;
 	slave->cs = cs;
+	slave->ctrlr = &spi_ctrlr;
 	return 0;
 }