spl: common: Move FAT funcs to a common file

Move the FAT functions to a common location for reuse.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
diff --git a/common/spl/Makefile b/common/spl/Makefile
index 5c0637b..c8d5963 100644
--- a/common/spl/Makefile
+++ b/common/spl/Makefile
@@ -16,4 +16,5 @@
 obj-$(CONFIG_SPL_ONENAND_SUPPORT) += spl_onenand.o
 obj-$(CONFIG_SPL_NET_SUPPORT) += spl_net.o
 obj-$(CONFIG_SPL_MMC_SUPPORT) += spl_mmc.o
+obj-$(CONFIG_SPL_FAT_SUPPORT) += spl_fat.o
 endif