spi: Add function callback to get configuration of SPI bus

Add a new callback to spi_ctrlr structure - get_config - to obtain
configuration of SPI bus from the controller driver. Also, move common
config definitions from acpi_device.h to spi-generic.h

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

Change-Id: I412c8c70167d18058a32041c2310bc1c884043ce
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/18337
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

src/drivers/spi/spi-generic.c

@@ -88,6 +88,16 @@ int spi_xfer(const struct spi_slave *slave, const void *dout, size_t bytesout,
 	return -1;
 }
 
+int spi_get_config(const struct spi_slave *slave, struct spi_cfg *cfg)
+{
+	const struct spi_ctrlr *ctrlr = slave->ctrlr;
+
+	if (ctrlr && ctrlr->get_config)
+		return ctrlr->get_config(slave, cfg);
+
+	return -1;
+}
+
 void __attribute__((weak)) spi_init(void)
 {
 	/* Default weak implementation - do nothing. */