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>

src/drivers/spi/spi-generic.c

@@ -0,0 +1,43 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2016 Google Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <spi-generic.h>
+#include <string.h>
+
+int spi_claim_bus(const struct spi_slave *slave)
+{
+	const struct spi_ctrlr *ctrlr = slave->ctrlr;
+	if (ctrlr && ctrlr->claim_bus)
+		return ctrlr->claim_bus(slave);
+	return 0;
+}
+
+void spi_release_bus(const struct spi_slave *slave)
+{
+	const struct spi_ctrlr *ctrlr = slave->ctrlr;
+	if (ctrlr && ctrlr->release_bus)
+		ctrlr->release_bus(slave);
+}
+
+int spi_xfer(const struct spi_slave *slave, const void *dout, size_t bytesout,
+	     void *din, size_t bytesin)
+{
+	const struct spi_ctrlr *ctrlr = slave->ctrlr;
+	if (ctrlr && ctrlr->xfer)
+		return ctrlr->xfer(slave, dout, bytesout, din, bytesin);
+
+	return -1;
+}