spl: spi: Move the generic SPI loader into common/spl

All the other SPL loaders are in this directory, so move the SPI one in
there too.

There are two board-specific SPI loaders (fsl and sunxi). These remain in
the drivers/mtd/spi directory, since they do not contain generic code.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/common/spl/Makefile b/common/spl/Makefile
index 5bd0b18..ed02635 100644
--- a/common/spl/Makefile
+++ b/common/spl/Makefile
@@ -25,4 +25,5 @@
 obj-$(CONFIG_SPL_EXT_SUPPORT) += spl_ext.o
 obj-$(CONFIG_SPL_SATA_SUPPORT) += spl_sata.o
 obj-$(CONFIG_SPL_DFU_SUPPORT) += spl_dfu.o
+obj-$(CONFIG_SPL_SPI_LOAD) += spl_spi.o
 endif