realtek: Convert incorrect v5.10 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/realtek/patches-5.10/311-add-i2c-mux-rtl9300-support.patch

@@ -1,3 +1,22 @@
+From f4bdb7fdccdfe3fa382abe77f72a16c2f2e6add0 Mon Sep 17 00:00:00 2001
+From: Birger Koblitz <git@birger-koblitz.de>
+Date: Sat, 11 Dec 2021 20:25:37 +0100
+Subject: [PATCH] realtek: Add support for RTL9300/RTL9310 I2C multiplexing
+
+The RTL9300/RTL9310 I2C controllers have support for 2 independent I2C
+masters, each with a fixed SCL pin, that cannot be changed. Each of these
+masters can use 8 (RTL9300) or 16 (RTL9310) different pins for SDA.
+This multiplexer directly controls the two masters and their shared
+IO configuration registers to allow multiplexing between any of these
+busses. The two masters cannot be used in parallel as the multiplex
+is protected by a standard multiplex lock.
+
+Submitted-by: Birger Koblitz <git@birger-koblitz.de>
+---
+ drivers/i2c/muxes/Kconfig                     |  9 +++++++
+ drivers/i2c/muxes/Makefile                    |  1 +
+ 2 files changed, 10 insertions(+)
+
 --- a/drivers/i2c/muxes/Kconfig
 +++ b/drivers/i2c/muxes/Kconfig
 @@ -99,6 +99,15 @@ config I2C_MUX_REG