spi: add DM_SPI_FLASH compatibility inline functions

To smoothly handle the transition from the legacy SPI FLASH
API to the driver model API, add the DM functions
as dummy inline functions.

Today, client code uses #if/#else conditionals, but it's better
to use if(IS_ENABLED()) to make sure all code builds fine
and avoid configuration hell, leaving the compiler remove
the dead code.

An example is cmd/sf, which could make use of those dummy
functions to drop the conditional compilation.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20241001-uboot-topic-dfu-sf-dt-v2-1-67f7acfa3ff5@linaro.org
[mkorpershoek: removed duplicate "the" from commit msg]
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
diff --git a/include/spi_flash.h b/include/spi_flash.h
index 10d19fd..2e703e8 100644
--- a/include/spi_flash.h
+++ b/include/spi_flash.h
@@ -139,6 +139,40 @@
 void sandbox_sf_unbind_emul(struct sandbox_state *state, int busnum, int cs);
 
 #else
+/* Compatibility functions for when DM_SPI_FLASH is disabled */
+static inline int spi_flash_probe_bus_cs(unsigned int busnum, unsigned int cs,
+					 struct udevice **devp)
+{
+	return -ENODEV;
+}
+
+static inline int spi_flash_read_dm(struct udevice *dev, u32 offset, size_t len,
+				    void *buf)
+{
+	return -ENODEV;
+}
+
+static inline int spi_flash_write_dm(struct udevice *dev, u32 offset, size_t len,
+				     const void *buf)
+{
+	return -ENODEV;
+}
+
+static inline int spi_flash_erase_dm(struct udevice *dev, u32 offset, size_t len)
+{
+	return -ENODEV;
+}
+
+static inline int spl_flash_get_sw_write_prot(struct udevice *dev)
+{
+	return -ENODEV;
+}
+
+static inline int spi_flash_std_probe(struct udevice *dev)
+{
+	return -ENODEV;
+}
+
 struct spi_flash *spi_flash_probe(unsigned int bus, unsigned int cs,
 		unsigned int max_hz, unsigned int spi_mode);