Merge patch series "nand: Add sandbox tests"

To quote the author:

This series tests raw nand flash in sandbox and fixes various bugs discovered in
the process. I've tried to do things in a contemporary manner, avoiding the
(numerous) variations present on only a few boards. The test is pretty minimal.
Future work could test the rest of the nand API as well as the MTD API.

Bloat (for v1) at [1] (for boards with SPL_NAND_SUPPORT enabled). Almost
everything grows by a few bytes due to nand_page_size. A few boards grow more,
mostly those using nand_spl_loaders.c. CI at [2].

[1] https://gist.github.com/Forty-Bot/9694f3401893c9e706ccc374922de6c2
[2] https://source.denx.de/u-boot/custodians/u-boot-clk/-/pipelines/18443

include/linux/mtd/mtd.h

@@ -552,8 +552,20 @@ unsigned mtd_mmap_capabilities(struct mtd_info *mtd);
 
 #ifdef __UBOOT__
 /* drivers/mtd/mtdcore.h */
+#if CONFIG_IS_ENABLED(MTD)
 int add_mtd_device(struct mtd_info *mtd);
 int del_mtd_device(struct mtd_info *mtd);
+#else
+static inline int add_mtd_device(struct mtd_info *mtd)
+{
+	return -ENOSYS;
+}
+
+static inline int del_mtd_device(struct mtd_info *mtd)
+{
+	return -ENOSYS;
+}
+#endif
 
 #ifdef CONFIG_MTD_PARTITIONS
 int add_mtd_partitions(struct mtd_info *, const struct mtd_partition *, int);