generic: Convert incorrect generic/5.10 patches

OpenWRT's developer guide prefers having actual patches so they an be
sent upstream more easily.

However, in this case, Adding proper fields also allows for `git am` to
properly function. Some of these patches are quite old, and lack much
traceable history.

This commit tries to rectify that, by digging in the history to find
where and how it was first added.

It is by no means perfect and also shows some patches that should have
been long gone.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>

target/linux/generic/pending-5.10/400-mtd-mtdsplit-support.patch

@@ -1,3 +1,25 @@
+From: Gabor Juhos <juhosg@openwrt.org>
+Subject: mtd: Add new Kconfig option for firmware partition split
+
+Add a new kernel config option for generic firmware partition
+split support and change the uImage split support to depend on
+the new option. Aslo rename the MTD_UIMAGE_SPLIT_NAME option to
+MTD_SPLIT_FIRMWARE_NAME to make it more generic.
+
+The patch is in preparation for multiple firmware format
+support.
+
+Submitted-by: Gabor Juhos <juhosg@openwrt.org>
+
+SVN-Revision: 38002
+---
+ drivers/mtd/Kconfig                           |  19 +
+ drivers/mtd/mtdpart.c                         | 144 +++++++++++++-----
+ include/linux/mtd/partitions.h                |   7 +
+ drivers/mtd/Makefile                          |   2 +
+ include/linux/mtd/mtd.h                       |  25 +
+ 5 files changed, 171 insertions(+), 25 deletions(-)
+
 --- a/drivers/mtd/Kconfig
 +++ b/drivers/mtd/Kconfig
 @@ -12,6 +12,25 @@ menuconfig MTD